Screen, display apparatus, screen use method, particle, particle layer, particle sheet, and light control sheet

ABSTRACT

There is provided a screen capable of sufficiently reducing speckles. A screen for displaying an image by being irradiated with a light beam from a projector, is provided with a plurality of particles each including a first part and a second part different in dielectric constant, a particle layer having the plurality of particles, and electrodes which form an electric field for driving the particles of the particle layer by applying a voltage to the particle layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/568,520, filed Oct. 23 2017, which in turn is the National Stageentry of International Application No. PCT/JP2016/062814, filed Apr. 22,2016, which designated the United States, the entireties of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present disclosure is related to a screen for displaying an image, adisplay apparatus having the screen, a screen use method, a particle, aparticle layer, a particle sheet, and a light control sheet.

BACKGROUND OF THE INVENTION

As disclosed in, for example, an International Publication 2012/033174pamphlet and Japanese Patent Laid-Open Publication Number 2008-310260, aprojector using a coherent light source is widely used. As a coherentlight beam, typically, a laser light beam oscillated by a laser lightsource is used. When a coherent light beam is used as an image lightbeam from the projector, speckles are observed on screen irradiated withthe image light beam. The speckles are perceived as a spotted pattern todegrade displayed image quality. In the International Publication2012/033174 pamphlet, for the purpose of reducing the speckles, theincidence angle of an image light beam incident on respective positionson a screen varies with time. As a result, scattering patterns having nocorrelation are overlapped on the screen to reduce the speckles.

SUMMARY OF THE INVENTION

As another method of reducing the speckles, a screen having diffusioncharacteristics that change with time is also considered to beeffective. In this respect, Japanese Patent Laid-Open Publication Number2008-310260 proposes a screen configured with an electronic paper. Inthe screen of Japanese Patent Laid-Open Publication Number 2008-310260,reflectance varies depending on the radiation position of an image lightbeam radiated in a raster scanning mode.

By changing the screen diffusion characteristics with time, specklereduction is achieved using a regular projector. It can be said thatthis is very useful concerning that the speckles can be reduced incombination with a projector, such as a raster-scanning projector, whichcannot adopt the method in the International Publication 2012/033174pamphlet.

However, the projector disclosed in Japanese Patent Laid-OpenPublication Number 2008-310260 has a problem in that its durability isnot enough and upsizing is difficult. As a result, the screen has notbeen widely used as a screen having a speckle reduction function. Thepresent disclosure is made in consideration of the above points and itspurpose is to provide a screen capable of sufficiently reducing speckleswith a method different from the conventional methods.

According to an aspect of the present disclosure, there is provided ascreen which displays an image by being irradiated with a light beamfrom a projector, including:

a plurality of particles including a first part and a second part;

a particle layer having the plurality of particles; and

electrodes which form an electric field driving the plurality ofparticles of the particle layer by applying a voltage to the particlelayer.

Dielectric constants of the first part and the second part of theparticles may be different from each other.

The particles may have a monochrome color.

Either of the first part or the second part of the particles may betransparent.

A volume ratio of the first part of the particles may be larger than avolume ratio of the second part of the particles.

The first part of the particles may have a light diffusing function andthe second part of the particles may have a light absorbing function.

The first part and the second part may be in contact with each other atan interface of a curved shape,

wherein the first part may be transparent, and

the particle layer may rotate the first part and the second part for atleast part of the plurality of particles by an alternating currentvoltage applied between the electrodes.

The first part may be disposed closer than the second part to anobserver of the screen.

The particle layer may rotate the first part and the second part withina rotation angle range less than 180 degrees in accordance with afrequency of the alternating current voltage applied between theelectrodes.

Volumes of the first part and the second part may be different from eachother.

The first part may be larger than the second part in volume,

wherein a surface of the second part, the surface being in contact withthe interface, may have a concave shape.

The first part may be smaller than the second part in volume,

wherein a surface of the second part, the surface being in contact withthe interface, may have a convex shape.

The second part may have a light diffusing function or a light absorbingfunction.

The second part may be a sphere or an oval sphere.

The projector may emit a coherent light beam,

wherein the particles may be configured to have higher reflectance to alight beam in a wavelength range of the coherent light beam than to alight beam outside the wavelength range of the coherent light beam.

The projector may emit a coherent light beam,

wherein the particles may be configured to have higher transmittance toa light beam in a wavelength range of the coherent light beam than to alight beam outside the wavelength range of the coherent light beam.

There may further be provided an absorbing layer to absorb the lightbeam outside the wavelength range of the coherent light beam.

The particles may include a pigment to selectively scatter the lightbeam in the wavelength range of the coherent light beam.

The particles may include a pigment or a dye to absorb the light beamoutside the wavelength range of the coherent light beam.

At least one layer included in the screen may include a pigment or a dyeto absorb the light beam outside the wavelength range of the coherentlight beam.

There may be included a third part in surface contact with the firstpart and with the second part, the third part controlling an incidentlight from the first part,

wherein the first part and the second part may be transparent, and

the particle layer may rotate the first to third parts for at least partof the plurality of particles by an alternating current voltage appliedbetween the electrodes.

The particle layer may rotate the first to third parts for at least partof the plurality of particles within a rotation angle range less than180 degrees in accordance with a frequency of the alternating currentvoltage applied between the electrodes.

The third part may scatter or reflect an incident light from the firstpart.

A thickness between the first face of and the second face of the thirdpart may be thinner than a maximum thickness of the first face of thefirst part in a direction of normal to the first face of the first part,and

a thickness between the first face of and the second face of the thirdpart may be thinner than a maximum thickness of the second face of thethird part in a direction of normal to the second face of the thirdpart.

The third part may be lower than the first part and the second part invisible light transmittance.

The first face and the second face may have a circular shape or an ovalshape and the third part may be a disc, an oval disc, a cylinder or anelliptic cylinder.

There may be provided a screen which displays an image by beingirradiated with a light beam from the projector, wherein at least partof the plurality of particles includes a plurality of diffusedcomponents dispersed in the first part and the second part.

There may be provided a Fresnel lens layer disposed on a surface side ofthe particle layer, the light beam being incident on the surface side.

There may be provided a screen which displays an image by beingirradiated with a light beam from a projector, including:

a plurality of particles each having a first part and a second part;

a particle layer having the plurality of particles; and

electrodes to form an electric field for driving the plurality ofparticles of the particle layer by applying a voltage to the particlelayer,

wherein the particles are rotatable by the electric field.

There may be provided a screen which displays an image by beingirradiated with a light beam from a projector, including:

a particle layer having a plurality of particles and a holder to holdthe particles, the particles being accommodated in cavities owned by theholder; and

electrodes to form an electric field for driving the plurality ofparticles of the particle layer by applying a voltage to the particlelayer,

wherein a single particle among the particles is accommodated in asingle cavity among the cavities.

There may be provided a photoelectric conversion panel-equipped screenincluding:

the above-described screen; and

a photoelectric conversion panel disposed on an opposite side of thescreen to a display-side surface of the screen, the photoelectricconversion panel being irradiated with the light beam passing throughthe screen.

There may be provided a photoelectric conversion panel-equipped screenincluding:

the above-described screen; and

a photoelectric conversion panel disposed aligned with the screen, thephotoelectric conversion panel being irradiated with a light beam fromthe projector.

The screen may be irradiated with a first light beam from the projector,

the photoelectric conversion panel may be irradiated with a second lightbeam from the projector, the second light beam being in a wavelengthband different from a wavelength band of the first light beam, and

conversion efficiency of the photoelectric conversion panel may bemaximum in the wavelength band of the second light beam.

The second light beam may be an invisible light beam.

There may further be provided a power supply device to generate anapplication voltage based on power generated by the photoelectricconversion panel and to apply the application voltage to the electrodes;and

a controller to control the application voltage,

wherein the controller may control the application voltage so as tooperate the particles in the particle layer.

The controller may control the application voltage so as to repeatedlyrotate the particles within an angular range less than 180°.

The controller may control at least orientations or positions of theparticles by the application voltage so that the first part covers atleast part of the second part from an observer's side along a directionof normal to the screen.

There may be provided a display apparatus including:

a projector to emit a coherent light beam; and

the above-described screen.

There may further be provided a power source to apply a voltage to theelectrodes of the screen; and

a controller to control an application voltage from the power source tothe electrodes,

wherein the controller may control the application voltage of the powersource so as to operate the particles in the particle layer.

The controller may control the application voltage so as to repeatedlyrotate the particles within an angular range less than 180°.

The controller may control at least orientations or positions of theparticles by the application voltage of the power source so that thefirst part covers at least part of the second part from an observer'sside along a direction of normal to the screen.

There may be provided a display apparatus including:

a projector to emit a light beam formed with a laser light beam; and

the above-described photoelectric conversion panel-equipped screen.

There may be provided a display apparatus including:

the above-described photoelectric conversion panel-equipped screen; and

a projector to radiate a first light beam formed with a laser light beamto the screen and simultaneously radiate a second light beam in awavelength band different from a wavelength band of the first light beamto the photoelectric conversion panel,

wherein conversion efficiency of the photoelectric conversion panel maybe maximum in the wavelength band of the second light beam.

There may be provided a method of using the above-described screen,including:

operating the particles in the particle layer while a light beam isbeing radiated to the screen.

The particles may be repeatedly rotated within an angular range lessthan 180° while a light beam is being radiated to the screen.

At least either of orientations and positions of the particles may becontrolled so that the first part covers at least part of the secondpart from an observer's side along a direction of normal to the screenwhile the screen is being irradiated with a light beam.

There may be provided a particle to be used for a screen which displaysan image by being irradiated with a light beam from a projector,including a first part and a second part different in dielectricconstant from each other.

The particle may have a monochrome color.

Either of the first part and the second part may be transparent.

A volume ratio of the first part may be larger than a volume ratio ofthe second part.

The first part may have a light diffusing function and the second partmay have a light absorbing function.

There may be provided the first part and the second part in contact witheach other at an interface of a curved shape,

wherein the first part may be transparent.

Volumes of the first part and the second part may be different from eachother.

The first part may be larger than the second part in volume,

wherein a surface of the second part, the surface being in contact withthe interface, may have a convex shape.

The first part may be smaller than the second part in volume,

wherein a surface of the second part, the surface being in contact withthe interface, may have a concave shape.

The second part may have a light diffusing or absorbing function.

The second part may be a sphere or an oval sphere.

According to an aspect of the present disclosure, there is provided aparticle to be used for a screen which displays an image using a lightbeam from a projector, including:

a transparent first part;

a transparent second part different from the first part in dielectricconstant; and

a third part in surface contact with the first part and with the secondpart, the third part controlling an incident light from the first part.

The third part may scatter or reflect an incident light beam from thefirst part.

A thickness between the first face of and the second face of the thirdpart may be thinner than a maximum thickness of the first face of thefirst part in a direction of normal to the first face of the first part,and

a thickness between the first face of and the second face of the thirdpart may be thinner than a maximum thickness of the second face of thethird part in a direction of normal to the second face of the thirdpart.

The third part may be lower than the first part and the second part invisible light transmittance.

The first face and the second face may have a circular shape or an ovalshape and the third part may be a disc, an oval disc, a cylinder or anelliptic cylinder.

There may be provided a particle layer including the above-describedparticle.

There may be provided a particle layer including the above-describedparticle.

According to an aspect of the present disclosure, there may be provideda light control sheet to control a light beam including a plurality ofparticles,

wherein the particles includes:

a transparent first part;

a transparent second part different from the first part in dielectricconstant; and

a third part in surface contact with the first part and with the secondpart, the third part controlling an incident light from the first part.

The third part may scatter, reflect or absorb an incident light beamfrom the first part.

A thickness between the first face of and the second face of the thirdpart may be thinner than a maximum thickness of the first face of thefirst part in a direction of normal to the first face of the first part,and

a thickness between the first face of and the second face of the thirdpart may be thinner than a maximum thickness of the second face of thethird part in a direction of normal to the second face of the thirdpart.

The third part may be lower than the first part and the second part invisible light transmittance.

The first face and the second face may have a circular shape or an ovalshape and the third part may be a disc, an oval disc, a cylinder or anelliptic cylinder.

There may be provided electrodes to form an electric field inside theparticle layer,

wherein the particle layer may rotate the first to third parts for atleast part of the particles by an alternating current voltage applied tothe electrodes.

According to the present disclosure, speckles can be sufficientlyreduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration for explaining an embodiment of the presentdisclosure and is a sectional view showing a display apparatus;

FIG. 2 is a longitudinal sectional view showing a screen of a displayapparatus;

FIG. 3 is a plan view showing a screen and an illustration forexplaining a method of radiating an image light beam onto the screenfrom a projector of a display apparatus;

FIG. 4 is an illustration for explaining an operation of a particle of aparticle layer;

FIG. 5 is an illustration for explaining an operation of the particle ofthe particle layer;

FIG. 6 is an illustration for explaining an operation of the particle ofthe particle layer;

FIG. 7 is a graph showing an example of a voltage applied to a screen;

FIG. 8 is an illustration for showing an modification of the particle;

FIG. 9 is an illustration for showing another modification of theparticle;

FIG. 10 is an illustration for showing still another modification of theparticle;

FIG. 11 is a longitudinal sectional view of a screen according to asecond embodiment;

FIG. 12 is an illustration for explaining an operation of the screenaccording to the second embodiment;

FIG. 13 is an illustration for explaining an operation of the screenaccording to the second embodiment;

FIG. 14 is an illustration for explaining an operation of the screenaccording to the second embodiment;

FIG. 15 is a longitudinal sectional view of a screen according to athird embodiment;

FIG. 16 is an illustration for explaining an operation of the screenaccording to the third embodiment;

FIG. 17 is an illustration for explaining an operation of the screenaccording to the third embodiment;

FIG. 18 is an illustration for explaining an operation of the screenaccording to the third embodiment;

FIG. 19 is an illustration for explaining a fourth embodiment and is asectional view showing a transparent-type display apparatus;

FIG. 20 is a longitudinal sectional view of a screen according to afifth embodiment;

FIG. 21 is an illustration for explaining an operation of the screenaccording to the fifth embodiment;

FIG. 22 is an illustration for explaining an operation of the screenaccording to the fifth embodiment;

FIG. 23 is an illustration for explaining an operation of the screenaccording to the fifth embodiment;

FIG. 24 is a longitudinal sectional view of a screen according to asixth embodiment;

FIG. 25 is a longitudinal sectional view of a light control sheetaccording to a seventh embodiment;

FIG. 26 is an illustration showing an example in which a first part hasa larger volume than a third part and a second part is disposed apartfrom the center of a particle;

FIG. 27 is an illustration for explaining an operation of a particle ofa particle layer according to an eighth embodiment;

FIG. 28 is an illustration for explaining an operation of the particleof the particle layer according to the eighth embodiment;

FIG. 29 is an illustration for explaining an operation of the particleof the particle layer according to the eighth embodiment;

FIG. 30 is an illustration for explaining a ninth embodiment and is asectional view showing a display apparatus;

FIG. 31 is a perspective view showing a solar cell-equipped screen andis an illustration showing a method of radiating an image light beamfrom a projector of a display apparatus to the screen;

FIG. 32 is a plan view showing a modification of the solar cell-equippedscreen and is an illustration showing a method of radiating a light beamfrom a projector of a display apparatus to the screen;

FIG. 33 is a plan view showing a modification of the solar cell-equippedscreen and is an illustration showing another example of the method ofradiating a light beam from a projector of a display apparatus to thescreen;

FIG. 34 is an illustration showing a modification of electrodes of ascreen;

FIGS. 35A, 35B and 35C are illustrations showing examples of a holderthat has a single cavity including a single particle; and

FIG. 36 is an illustration for explaining a method of measuring whethera particle in a screen rotates.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present disclosure will be explainedwith reference to the drawings. In the accompanying drawings of thepresent specification, for simplicity of drawings and easyunderstanding, the scale, the ratio of height to width, etc. areappropriately modified or enlarged from actual ones.

First Embodiment

FIGS. 1 to 6 are illustrations for explaining a first embodiment of thepresent disclosure. FIG. 1 is an illustration showing a displayapparatus. FIG. 2 is a longitudinal sectional view showing a screen.FIG. 3 is an illustration for explaining a radiation method of an imagelight beam onto the screen. FIGS. 4 to 6 are illustrations forexplaining an operation of the screen. FIG. 7 is a graph showing anexample of a voltage applied to the screen from a power source.

As shown in FIGS. 1 to 6, a display apparatus 10 has a projector 20 anda screen 40 to be irradiated with an image light beam from the projector20. As described later, the screen 40 is capable of changing with timethe diffusion characteristics that affect an incident light beam. Inthis way, speckles become inconspicuous. In relation to such function ofthe screen 40, the display apparatus 10 further has a power source 30and a controller 35. The power source 30 applies a voltage to the screen40. The controller 35 adjusts the applied voltage from the power source30 to control the mode of the screen 40. Moreover, the controller 35controls the operation of the projector 20. As an example, thecontroller 35 is a general-purpose computer.

The projector 20 projects a light beam for forming an image, that is, animage light beam, onto the screen 40. In the example shown, theprojector 20 has a coherent light source 21 for oscillating a coherentlight beam and a scanning device (not shown) for adjusting an opticalpath of the coherent light source 21. The coherent light source 21 is,as a typical example, made up of a laser light source for oscillating alaser light beam. The coherent light source 21 may have a plurality ofcoherent light sources for generating light beams in wavelength rangesdifferent from one another.

In the example shown, the projector 20 projects a coherent light beamonto the screen 40 in a raster scanning mode. As shown in FIG. 3, theprojector 20 projects the coherent light beam onto the screen 40 so asto scan the entire area of the screen 40. Scanning is performed at highspeeds. In accordance with an image to be formed, the projector 20 stopsemission of the coherent light beam from the coherent light source 21.In other words, the coherent light beam is projected onto only aposition on the screen 40 at which the image is to be formed. As aresult, the image is formed on the screen 40. The operation of theprojector 20 is controlled by the controller 35.

Subsequently, the screen 40 will be explained. In the example shown inFIGS. 1 and 2, the screen 40 has a particle sheet 50 having a pluralityof particles, and electrodes 41 and 42 connected to the power source 30.The first electrode 41 is spread in a planar shape over one main surfaceof the particle sheet 50. The second electrode 42 is spread in a planarshape over the other main surface of the particle sheet 50. Moreover,the shown screen 40 has a first cover layer 46 that covers the firstelectrode 41 to form one outermost surface of the screen 40 and a secondcover layer 47 that covers the second electrode 42 to form the otheroutermost surface of the screen 40.

In the example shown, the screen 40 is a reflection-type screen. Theprojector 20 projects an image light beam onto a display-side surface 40a made up of the first cover layer 46. The image light beam passesthrough the first cover layer 46 and the first electrode 41 of thescreen 40 and, thereafter, is reflected on the particle sheet 50 bydiffuse reflection. As a result, an observer situated to face thedisplay-side surface 40 a of the screen 40 can observe an image.

The first electrode 41 and the first cover layer 46 through which theimage light beam passes are transparent. It is preferable that the firstelectrode 41 and the first cover layer 46 each have transmittance of 80%or higher in a visible light range and, more preferably 84% or higher.Visible light transmittance is defined as an average value oftransmittance at wavelengths measured in a measurement wavelength rangefrom 380 nm to 780 nm using a spectrophotometer (“UV-3100PC” made byShimadzu Corporation, a product conforming to JISK0115).

As a conductive material to make up the first electrode 41, ITO (IndiumTin Oxide), InZnO (Indium Zinc Oxide), Ag nanowire, carbon nanotube,etc. can be used. The first cover layer 46 is a layer for protecting thefirst electrode 41 and the particle sheet 50. The first cover layer 46can be formed with transparent resin, for example, polyethyleneterephthalate excellent in stability, or polycarbonate, cycloolefinpolymer, etc.

The second electrode 42 can be formed in the same manner as the firstelectrode 41. The second cover layer 47 can be formed in the same manneras the first cover layer 46. However, the second electrode 42 is notrequired to be transparent. Therefore, the second electrode 42, can, forexample, be formed with a metal thin film of aluminum, copper, etc. Thesecond electrode 42 made of a metal film can also function as areflective layer to reflect an image light beam in the reflective-typescreen 40. The second cover layer 47 can be formed in the same manner asthe first cover layer 46.

Subsequently, the particle sheet 50 will explained. As shown in FIG. 2,the particle sheet 50 has a pair of base members 51 and 52, and aparticle layer 55 disposed between the pair of base members 51 and 52.The first base member 51 holds the first electrode 41 and the secondbase member 52 holds the second electrode 42. The particle layer 55 issealed between the first base member 51 and the second base member 52.The first base member 51 and the second base member 52 can be formedwith a material having strength to be able to function to seal theparticle layer 55 and have a function as a holder of the electrodes 41and 42, and the particle layer 55, which is, for example, a polyethyleneterephthalate resin film. In the embodiment shown, the screen 40 is areflective-type screen in which an image light beam passes through thefirst base member 51. Therefore, the first base member 51 is transparentand preferably has visible light transmittance at the same level as thefirst electrode 41 and the first cover layer 46.

Subsequently, the particle layer 55 will be explained. As shown well inFIG. 2, the particle layer 55 has a large number of particles 60 and aholder 56 for holding the particles 60. The holder 56 holds theparticles 60 so as to be operable. In the example shown, the holder 56has a large number of cavities 56 a. Each particle 60 is accommodated ineach cavity 56 a. The inner size of each cavity 56 a is larger than theouter size of the particle 60 in the cavity 56 a. Therefore, theparticle 60 is operable inside the cavity 56 a. The holder 56 swells bya solvent 57. The cavity 56 a is filled with a solvent 57 between theholder 56 and the particles 60. By means of the holder 56 swelling withthe solvent 57, a smooth operation of the particles 60 can be securedstably. Hereinbelow, the holder 56, the solvent 57, and the particles 60will be explained in order.

First of all, the holder 56 and the solvent 57 will be explained. Thesolvent 57 is used for a smooth operation of the particles 60. When theholder 56 swells, the solvent 57 is held inside each cavity 56 a. It ispreferable that the solvent 57 has low polarity so as not to obstruct anoperation of the particles 60 in response to electric fields. As thelow-polarity solvent 57, a variety of types of materials that makesmooth the operation of the particles 60 can be used. As examples of thesolvent 57, dimethyl silicon oil, an isoparaffin-based solvent,straight-chain paraffin-based solvent, and straight-chain alkane, suchas dodecane and tridecane, can be listed up.

Subsequently, the holder 56 can be formed, as an example, with anelastomer sheet made of elastomer. The holder 56 as the elastomer sheetis capable of making the above-described solvent 57 swell. As a materialof the elastomer sheet, silicon resin, (slightly crosslinked) acrylicresin, (slightly crosslinked) styrene resin, polyolefin resin, etc. canbe listed up, as examples.

In the example shown, the cavities 56 a are distributed at high densityin the holder 56, in the plane direction of the screen 40. The cavities56 a are also distributed in the direction of normal nd to the screen40. In the example shown, a group of the cavities 56 a spread in aplanar shape are aligned in three layers in a depth direction of thescreen 40.

Subsequently, the particles 60 will be explained. The particles 60 havea function of changing the travel direction of an image light beamprojected from the projector 20. In the example shown, the particles 60have a function of diffusing the image light beam, especially, bydiffuse reflection.

Each particle 60 includes a first part 61 and a second part 62 differentin dielectric constant. Therefore, when this particle 60 is placed in anelectric field, an electron dipole moment is generated in the particle60. In this occasion, the particle 60 operates in such a manner that avector of the electron dipole moment is oriented in a complete oppositedirection of a vector of the electric field. Therefore, when a voltageis applied between the first electrode 41 and the second electrode 42 sothat an electric field is generated in the particle sheet 50 locatedbetween the first electrode 41 and the second electrode 42, the particle60 operates in each cavity 56 a in such a manner that the particle 60takes a stable posture with respect to the electric field, that is, astable position and orientation with respect to the electric field. Thescreen 40 changes its diffusion wavefront in accordance with theoperation of the particles 60 having a light diffusion function.

The particles 60 each including the first part 61 and the second part 62different in dielectric constant can be produced by a variety of methodsincluding known techniques. The particles 60 can be produced by, forexample, a method to align spherical particles of organic or inorganicmatters in a single layer using an adhesive tape or the like, withdeposition of a resin component layer or of an inorganic matter layer,to be charged with positive and negative electricity different from theparticles, on a hemisphere of each particle (a deposition method, forexample, Japanese Patent Laid-Open No. S56-67887), a method using arotary disc (for example, Japanese Patent Laid-Open No. H6-226875), amethod to make droplets of different dielectric constants in contactwith each other in air by a splaying method or an ink jet method to forma single droplet (for example, Japanese Patent Laid-Open No.2003-140204), and a microchannel production method proposed inJP2004-197083A. As proposed in JP2004-197083A, the first part 61 and thesecond part 62 different from each other in dielectric constant can beformed with materials different in charging characteristics from eachother. The microchannel production method is to use a continuous phaseand a spheroidizing phase having an oily/aqueous (O/W type) oraqueous/oily (W/O type) relationship with each other and to sequentiallydischarge a continuous phase including two kinds of materials differentin charging characteristics from each other, from a first microchannel,through which the continuous phase is transferred, into thespheroidizing phase of a fluid medium that flows through a secondmicrochannel, thereby producing bipolar particles 60 that are two-layerpolymer particles 60 and have polarities of (±) in charge.

In the microchannel production method, in an oily or aqueous fluidmedium including polymerizable resin components, polymerizable resincomponents, which are in the continuous phase that is a separated phaseinsoluble to the fluid medium, are formed, using polymerizable monomersthat are charged with positive and negative polarities different fromeach other, and are transferred to the first microchannel. Thecontinuous phase is then discharged sequentially or intermittently intoan aqueous or oily spheroidizing phase that flows in the secondmicrochannel. The matters discharged into the spheroidizing phase arespheroidized during a series of discharge, dispersion, and transfer inthe microchannels. Therefore, the particles 60 are prepared bypolymerizing and hardening polymerizable resin components in thespheroidized matters while the polymerizable resin components are beingsubjected to UV radiation and/or heating.

As the polymerizable resin components (or the polymerizable monomers) tobe used for particles 60, monomer types, by which the particles 60 havean tendency of being charged with polarities of (−) and (+) depending onthe kinds of a functional group or substituent of the polymerizablemonomers to be used for particles 60, can be listed up. Therefore, whenat least two kinds of monomers are used as the polymerizable resincomponents, it is preferable that a plurality of monomers having atendency of being charged with the same polarity are combined in anappropriate manner on condition that the tendency of being charged withpolarities of (+) and (−) is well understood. In addition, an additivesuch as a polymerization initiator, besides the monomers, is added afterthe additive is adjusted so as not to loose chargeability in the entirematerial.

In the polymerizable resin components (or the polymerizable monomers)having at least one kind of functional group and/or substituent inmolecules, as the functional group or substituent, for example, acarbonyl group, a vinyl group, a phenyl group, an amino group, an amidegroup, an imide group, a hydroxyl group, a halogen group, a sulfonicacid group, an epoxy group, and urethane coupling can be listed up. Asingle monomer type having such functional groups or substituents in thepolymerizable monomers can be appropriately used. Or two or more monomertypes having such functional groups or substituents in the polymerizablemonomers can be combined to be appropriately used.

As a polymerizable monomer having a tendency of being charged with apolarity of (−) and a polymerizable monomer having a tendency of beingcharged with a polarity of (+), those described in JP2004-197083A can beused, and hence the explanation thereof is omitted in this description.

When producing the particles 60 with the microchannel production method,by adjusting the speed, the joint direction, etc., in the case where thetwo kinds of polymerizable resin components that constitute thecontinuous phase are joined to each other, and by adjusting the speed,the discharge direction, etc., in the case where the continuous phase isdischarged into the spheroidizing phase, the outer shape of the obtainedparticles 60, the interface shape between the first part 61 and thesecond part 62 of each particle 60, etc. can be adjusted. In the exampleof the particle 60 shown in FIGS. 4 to 6, the volume ratio of the firstpart 61 and the volume ratio of the second part 62 are the same as eachother. Moreover, in the example of the particle 60 shown in FIGS. 4 to6, the interface between the first part 61 and the second part 62 isformed into a planar shape. And the particle 60 shown in FIGS. 4 to 6 isa sphere. That is, in the particle 60 shown in FIGS. 4 to 6, the firstpart 61 and the second part 62 are each a hemisphere.

When the two kinds of polymerizable resin components that constitute thecontinuous phase include diffused components, the first part 61 and thesecond part 62 of the particle 60 can be given an internal diffusionfunction. In the example shown in FIGS. 4 to 6, the first part 61 of theparticle 60 has a first main part 66 a and a first diffused component 66b diffused in the first main part 66 a. In the same manner, the secondpart 62 has a second main part 67 a and a second diffused component 67 bdiffused in the second main part 67 a. In other words, the sphereparticle 60 shown in FIGS. 4 to 6 is capable of developing a diffusionfunction to a light beam travelling inside the first part 61 and a lightbeam travelling inside the second part 62. Here, the diffused components66 b and 67 b are components capable of exerting an action to change thetravel direction of a light beam travelling inside the particle 60 byreflection, refraction, etc. Such light diffusion function (lightscattering function) of the diffused components 66 b and 67 b is givenby, for example, forming the diffused components 66 b and 67 b withmaterials having refractive indexes different from those of thematerials that constitute the main parts 66 a and 67 a of the particle60 or with materials capable of exerting a reflection operation to alight beam. As the materials having refractive indexes different fromthose of the materials that constitute the main parts 66 a and 67 a,resin beads, glass beads, a metal compound, a porous material containinga gas, and mere babbles are listed up as examples.

In the example shown, the particles 60 have a monochrome color. In otherwords, the first part 61 and the second part 62 have the same color. Thecolor of the first part 61 and the second part 62 can be adjusted byadding a coloring material such as a pigment and a dye to the first part61 and the second part 62. As the pigment and the dye, a variety ofknown pigments and dyes can be used. As examples, pigments disclosed inJP2005-99158A and JP2780723B, pigments or dyes disclosed in JP5463911Bcan be used.

The monochrome color to be used for the particles 60 is meant to have auniform color, the level of uniformness being to the extent that colorchange on the screen 40 cannot be perceived by an observer who observesthe display-side surface 40 a of the screen 40 with normal power ofobservation even if the particles 60 operate in the particle sheet 50 inthe state where no image display is performed on the screen 40. In otherwords, if the display-side surface 40 a of the screen 40 in the statewhere the first part 61 of each particle 60 is oriented toward thedisplay-side surface 40 a of the screen 40 and the display-side surface40 a of the screen 40 in the state where the second part 62 of eachparticle 60 is oriented toward the display-side surface 40 a of thescreen 40 are perceived as having the same color with normal power ofawareness of the observer in the state where no image display isperformed on the screen 40, it can said that the particles 60 have amonochrome color. In more specifically, it is preferable that, betweenthe display-side surface 40 a of the screen 40 in the state where thefirst part 61 of each particle 60 is oriented toward the display-sidesurface 40 a of the screen 40 and the display-side surface 40 a of thescreen 40 in the state where the second part 62 of each particle 60 isoriented toward the display-side surface 40 a of the screen 40, a colordifference ΔE*ab(=[(ΔL*)²+(Δa*)²+(Δb*)²]^(1/2)) is 1.5 or smaller. Thecolor difference ΔE*ab is defined as a value specified based onbrightness L*, and chromaticity a* and b* in the L*a*b* color appearancesystem measured using a colorimeter (CM-700d) made by Konica Minolta inconformity with JIS Z 8730. When the screen 40 is a reflection type,evaluation is made with a value of ΔE*ab specified based on brightnessL*, and chromaticity a* and b* of a reflected light beam. When thescreen 40 is a transmission type, evaluation is made with a value ofΔE*ab specified based on brightness L*, and chromaticity a* and b* of atransmitted light beam.

The particle layer 55, the particle sheet 50, and the screen 40 can beproduced as described below as an example.

The particle layer 55 can be produced by a production method disclosedin JP1-28259A. That is, first of all, an ink in which the particles 60are dispersed in polymerizable silicon rubber is prepared. Subsequently,the ink is stretched by a coater or the like and polymerized by heatingor the like to be formed into a sheet. By these steps, the holder 56that holds the particles 60 is obtained. Subsequently, the holder 56 isdipped into the solvent 57 such as silicon oil for a certain period oftime. When the holder 56 swells, a gap filled with the solvent 57 isformed between the holder 56 made of silicon rubber and each particle60. As a result, the cavities 56 a that accommodate the solvent 57 andthe particles 60 are defined. As described above, the particle layer 55can be produced.

Subsequently, by a production method disclosed in JP2011-112792A, thescreen 40 can be produced using the particle layer 55. First of all, theparticle layer 55 is covered with the pair of base members 51 and 52,and sealed by lamination or using an adhesive or the like. In this way,the particle sheet 50 is produced. Subsequently, the first electrode 41and the second electrode 42 are disposed on the particle sheet 50, andfurthermore, the first cover layer 46 and the second cover layer 47 aredisposed thereon to obtain the screen 40.

Subsequently, an operation in displaying an image using this displayapparatus 10 will be explained.

First of all, under control by the controller 35, the coherent lightsource 21 of the projector 20 oscillates a coherent light beam. Thelight beam from the projector 20 is subjected to optical pathadjustments by a scanning device not shown and is radiated onto thescreen 40. As shown in FIG. 3, the scanning device not shown adjusts theoptical path of the light beam so that the light beam scans thedisplay-side surface 40 a of the screen 40. Emission of the coherentlight beam by the coherent light source 21 is controlled by thecontroller 35. In accordance with an image to be displayed on the screen40, the controller 35 stops the emission of the coherent light beam fromthe coherent light source 21. The operation of the scanning deviceincluded in the projector 20 is performed at a high speed to the extentthat it cannot be resolved by human eyes. Therefore, the observerobserves simultaneously light beams radiated onto respective points onthe screen 40 at a given time interval.

A light beam projected onto the screen 40 passes through the first coverlayer 46 and the first electrode 41, and then reaches the particle sheet50. The light beam is reflected on the particles 60 of the particlesheet 50 by diffuse reflection and emitted toward several directions inthe observer's side of the screen 40. Therefore, at respective points ofthe screen 40 in the observer's side, reflected light beams fromrespective points on the screen 40 can be observed. As a result, animage corresponding to an area irradiated with the coherent light beamson the screen 40 can be observed.

The coherent light source 21 may include a plurality of light sourcesthat emit coherent light beams of wavelengths different from oneanother. In this case, the controller 35 controls a light sourcecorresponding to a light beam of each wavelength independently from theother light sources. As a result, it is possible to display a colorimage on the screen 40.

When a coherent light beam is used to form an image on a screen,speckles of a spot pattern are observed. One cause of the speckles isconsidered that, after a coherent light beam, a typical example of whichis a laser beam, is diffused on the screen, the coherent light beamgenerates an interference pattern on an optical sensor (retinas in thecase of human beings). Above all, when a coherent light beam is radiatedonto the screen by raster scanning, the coherent light beam is incidenton respective points on the screen from a constant incidence direction.Therefore, when the raster scanning is adopted, speckle wavefrontsgenerated at the respective points on the screen are unchanged as longas the screen does not swing, and when the speckle pattern is viewed bythe observer, the image quality of a displayed image is drasticallydegraded.

To the contrary, the screen 40 of the display apparatus 10 according tothe present embodiment changes diffusion wavefront with time. When thediffusion wavefront on the screen 40 changes, speckle patterns on thescreen 40 change with time. When the diffusion wavefront changes withtime at a sufficiently high speed, the speckle patterns are overlappedone another and averaged to be observed by the observer. As a result,speckles become inconspicuous.

The shown screen 40 has a pair of electrodes 41 and 42. The pair ofelectrodes 41 and 42 are electrically connected to the power source 30.The power source 30 is capable of applying a voltage to the pair ofelectrodes 41 and 42. When the voltage is applied between the pair ofelectrodes 41 and 42, an electric field is formed in the particle sheet50 located between the pair of electrodes 41 and 42. The particle layer55 of the particle sheet 50 holds the particles 60 so as to be operable,each including the first part 61 and the second part 62 different indielectric constant. Since the particles 60 have been charged or adipole moment is generated when an electric field is formed in at leastthe particle layer 55, the particles 60 operate in accordance with avector of the formed the electric field. When the particles 60 operate,which have a function of changing a light travel direction, such as, areflection function and a diffusion function, as shown in FIGS. 4 to 6,the diffusion characteristics of the screen 40 change with time. As aresult, speckles become inconspicuous. In FIGS. 4 to 6, and FIGS. 8 and10 which will be referred to later, a sign “La” is an image light beamradiated from the projector 20 to the screen 40 and signs “Lb” are imagelight beams diffused by the screen 40.

Concerning the difference in dielectric constants between the first part61 and the second part 62 of each particle 60, it is enough for thedielectric constants to be different to the extent that a specklereducing function can be exerted. Therefore, whether the dielectricconstants between the first part 61 and the second part 62 of theparticle 60 are different from each other can be determined by whetherthe particle 60 held operable can operate in accordance with the changein electric field vector.

The operating principle of the particles 60 to the holder 56 is tochange the orientation and position of each particle 60 so that theelectric charge or dipole moment of the particle 60 has a stablepositional relationship with an electric field vector. Therefore, when aconstant electric field is continuously applied to the particle layer55, the operation of the particle 60 stops after a certain period oftime. On the other hand, in order to make speckles inconspicuous, it isrequired that the operation of the particle 60 to the holder 56continues. Accordingly, the power source 30 applies a voltage so that anelectric field formed in the particle layer 55 varies with time. In theexample shown, the power source 30 applies a voltage between the pair ofelectrodes 41 and 42 so as to invert the vector of an electric fieldgenerated in the particle sheet 50. For example, in an example shown inFIG. 7, the power source 30 repeatedly applies a voltage X[V] and avoltage −Y[V] to the pair of electrodes 41 and 42 of the screen 40.Together with such application of an inverted electric field, as anexample, the particle 60 can repeatedly operate between the states ofFIGS. 6 and 7 with the state of FIG. 5 as a center state.

The control of an application voltage in FIG. 7 is extremely easy. Aboveall, in the example shown in FIG. 7, the voltage X[V] and the voltage−Y[V] have the same absolute value, under extremely simple control.Nevertheless, the application voltage shown in FIG. 7 is just anexample. The voltage X[V] and the voltage −Y[V] may have differentabsolute values. Moreover, voltages of three or more different valuesmay be applied. Furthermore, the application voltage may continuouslyvary by adopting an ordinary alternating current voltage, for example.

The particles 60 are accommodated in the cavities 56 a formed in theholder 56. In the example shown in FIGS. 4 to 6, each particle 60 has analmost sphere outer shape. Each cavity 56 a that accommodates theparticle 60 has an almost sphere inner shape. Therefore, the particle 60can perform rotational vibration having a rotation axis line ra, as acenter, which extends in a direction perpendicular to the drawing sheetsof FIGS. 4 to 6. Depending on the size of the cavity 56 a thataccommodates the particle 60, the particle 60 performs, not only therepeated rotary motion, but also translational motion. The cavity 56 ais filled with the solvent 57. The solvent 57 makes smooth the operationof the particle 60 to the holder 56.

As shown in FIGS. 35A to 35C, each cavity 56 a owned by the holder 56 inthe particle layer 55 may be configured to include a single particle 56.FIG. 35A shows a holder 56 in which a single cavity 56 a includes asingle particle 56. FIG. 35B shows a holder 56 in which two cavities 56a 1 and 56 a 2 coupled to each other include a single particle 60-1 and60-2, respectively. The particles 60-1 and 60-2 are subjected to movablerange restriction by the associated cavities 56 a 1 and 56 a 2,respectively. FIG. 35C shows a holder 56 in which three cavities 56 a 1,56 a 2, and 56 a 3 coupled to one another include a single particle60-1, 60-2, and 60-3, respectively. The particles 60-1, 60-2, and 60-3are subjected to movable range restriction by the associated cavities 56a 1, 56 a 2, and 56 a 3, respectively. As described above, even though aplurality of cavities are coupled to one another, when the movableranges of a plurality of particles are arranged without overlapping oneanother, the cavities owned by the holder 56 can each be regarded asbeing configured to include a single particle.

There is no restriction on the internal diameter of each cavity as longas it is larger than the outer diameter of a particle contained in thecavity. For example, the internal diameter of each cavity may be set tobe 1.1 times to 1.3 times as large as the outer diameter of a particlecontained in the cavity.

In the present embodiment described above, the screen 40 has theparticle layer 55 that has the particles 60 each including the firstpart 61 and the second part 62 that are different in dielectricconstant, and has the electrodes 41 and 42 that form an electric fieldfor driving the particles 60 of the particle layer 55, by being appliedwith a voltage. In the screen 40, when a voltage is applied between thefirst electrode 41 and the second electrode 42, an electric field isformed in the particle layer 55. In this occasion, the particles 60operate in accordance with the formed electric field. When the particles60 operate, which have a function of changing a light travel direction,such as, a reflection function and a diffusion function, the diffusioncharacteristics of the screen 40 change with time. Therefore, while alight beam is being radiated onto the screen 40, by forming the electricfield in the particle layer 55 to operate the particles 60, it ispossible to efficiently make the speckles inconspicuous. It isrelatively easy to produce such screen 40, for example, using theabove-described production method. In addition, the screen 40 issuitable for a large screen and excellent in durability and operationalstability, and furthermore, easily-controllable.

Moreover, according to the present embodiment, each particle 60including the first part 61 and the second part 62 that are different indielectric constant is formed to have a monochrome color. Therefore,even though at least one of the orientation and position of the particle60 changes, the screen 40 has a constant color. Accordingly, whendisplaying an image, it is not perceived that the tone of the screen 40is changed. As a result, it is also possible to efficiently avoid imagequality degradation in accordance with color change in the screen 40.The particles 60 operable in an electric field and having a monochromecolor can be produced by forming the first part 61 and the second part62 from synthetic resins of the same kind and by mixing a chargingadditive into one of the first part 61 and the second part 62.Accordingly, such useful particles 60 for the screen 40 can be easilyproduced.

Furthermore, according to the present embodiment, while a light beam isbeing radiated onto the screen 40, the particles 60 can be repeatedlyrotated in the particle layer 55. In other words, the particles 60 canoperate to effectively change the diffusion fronts in an extremely smallspace. Nevertheless, since it is possible to keep the screen diffusioncharacteristics constant, it is possible to reduce speckles only, whilekeeping parameters constant, such as screen brightness. Therefore, byrepeatedly rotating the particles 60, while realizing a thin particlelayer 55 and a thin screen 40, speckles can be effectively madeinconspicuous. When repeatedly rotating each particle 60, its angularrange is preferably less than 180° as shown in FIGS. 4 to 6. In thiscase, either of the first part 61 and the second part 62 can mainly besituated on the observer's side. In other words, while a light beam isbeing radiated onto the screen 40, it is possible that the first part 61covers at least part of the second part 62 when viewed from theobserver's side along the direction of normal nd to the screen 40.Accordingly, even if the first part 61 and the second part 62 do nothave exactly the same color, during image display while operating theparticles 60, the change in tone of the screen 40 can be hardlyperceived.

It can be checked by the following method that the particles 60 arerotating. In a specific manner, as shown in FIG. 36, a coherent lightbeam is radiated onto the screen 40 from a light source 111. A coherentlight beam that has passed through or reflected by the screen 40, thatis, diffused light beams, is radiated onto a screen 112 formeasurements. Then, the light intensity distribution on the screen 112(measuring surface) for measurements is measured by a camera 113. Or,without using the screen for measurements, a two-dimensional lightintensity distribution of the diffused light beams may be directlymeasured by a two-dimensional array sensor.

While the particles 60 are being driven to rotate, the wavefronts oflight beams diffused by the particles 60 change and also thetwo-dimensional light intensity distribution on the measuring surfacechanges with time. Therefore, in the case where the operation of theparticles 60 is above-described translational motion only, the movementof the two-dimensional light intensity distribution on the measuringsurface is translational shift only. Accordingly the configuration ofthe diffusion wavefront itself does not change.

When the operation of the particles 60 is rotational motion, since theposition and angle of the diffusion surface change due to rotation ofeach particle 60, that is, wavefronts from different parts of thediffusion surface, the configuration of the diffusion wavefront from theparticle 60 itself changes. Therefore, by a measuring method such asshown in FIG. 36, it is relatively easy to detect whether the particles60 in the screen 40 are rotating.

As explained in the above-described embodiment, by varying the voltageto the pair of electrodes 41 and 42, the particles 60 can be operated.And, by adjusting the variation range, center voltage, etc. of theapplication voltage, it is possible to control the repeated operationrange of the particles 60, and the orientations and positions of theparticles 60 at the center of the operation range.

To the above-described embodiment, it is possible to make a variety ofchanges. Hereinafter, with reference to the drawings, an example ofmodification will be explained. In the following explanation and thedrawings to be used in the following explanation, the same signs asthose to the corresponding elements in the above-described embodimentare used and the duplicate explanation is omitted.

In the above-described embodiment, the example in which the first part61 and the second part 62 have the same color is shown, however, theembodiment is not to be restricted to this example. Either of the firstpart 61 and the second part 62 may be transparent. In the particle 60shown in FIG. 8, the first part 61 is formed to be transparent. Theparticle 60 shown in FIG. 8 is capable of changing the travel directionof a light beam incident on the particle 60 by reflection or refractionat the interface between the first part 61 and the second part 62, bydiffusion at the second part 62, and by reflection or refraction at thesurface of the particle 60. The color of such particle 60 can beperceived as the color of the second part 62 because the first part 61is transparent. Therefore, even though the orientation, posture, andposition of the particle 60 change, the screen 40 has a constant color.Accordingly, when displaying an image, there is no possibility that thetone of the screen 40 is perceived to change. As a result, it ispossible to efficiently avoid image quality degradation in accordancewith color change in the screen 40.

The first part 61 and the second part 62 of the particle 60 may be, asshown in FIG. 9, different in volume ratio. In other words, the volumeratio of the first part 61 that occupies the particle 60 and the volumeratio of the second part 62 that occupies the particle 60 may bedifferent from each other. In the particle 60 shown in FIG. 9, thevolume ratio of the first part 61 is larger than the volume ratio of thesecond part 62. In the case of using such particle 60, while a lightbeam is being radiated onto the screen 40, it becomes easy for the firstpart 61 to cover at least part of the second part 62 when viewed fromthe observer's side along the direction of normal nd to the screen 40.Moreover, when the second part 62 shifts to the position indicated by atwo-dot chain line along with the rotary motion of the particle 60, thefirst part 61 can cover the second part 62 when viewed from theobserver's side along the direction of normal nd to the screen 40.Accordingly, even if the first part 61 and the second part 62 do nothave exactly the same color, during image display while operating theparticle 60, it is possible that the change in tone of the screen 40 ishardly perceived.

Moreover, in the case where, by drive control of the particle 60, thechange in tone of the screen 40 can hardly be perceived withoutreceiving a large effect of difference in color between the first part61 and the second part 62, either of the first part 61 and the secondpart 62 may have a light absorbing function. In an example shown in FIG.10, the first part 61 has the light diffusion characteristics while thesecond part 62 has the light absorbing function. The light absorbingfunction of the second part 62 can be developed when, as an example, thesecond part 62 includes a light-absorbing coloring material,specifically, a pigment such as carbon black and titan black. In theparticle 60 shown in FIG. 10, a light beam Lc incident from a directiondifferent from the direction of an image light beam La from theprojector 20 can be absorbed by the second part 62. The light beam to beabsorbed by the second part 62 may, for example, be an ambient lightbeam from an illumination apparatus 90 (refer to FIG. 1) present in theplace where the display apparatus 10 is installed. By selecting andabsorbing the light beam Lc except for the image light beam La incidenton the screen 40, without loosing the brightness of a displayed image,it is possible to efficiently improve the contrast of the displayedimage.

Second Embodiment

FIGS. 11 to 14 are illustrations for explaining a second embodiment ofthe present disclosure. FIG. 11 is a longitudinal sectional view of ascreen 40 according to the second embodiment. FIGS. 12 to 14 areillustrations for explaining an operation of the screen 40 of FIG. 11.

Like shown in FIG. 1, the display apparatus 10 according to the secondembodiment has a projector 20 and a screen 40 to be irradiated with animage light beam from the projector 20. As described later, the screen40 is capable of changing with time the diffusion characteristics thataffect an incident light beam. In this way, speckles becomeinconspicuous. The projector 20 according to the second embodiment, likeshown in FIG. 3, projects a coherent light beam onto the screen 40 inthe raster scanning mode.

Subsequently, the screen 40 according to the second embodiment will beexplained. In the example shown, the screen 40 has a particle sheet 50having a plurality of particles 60, and transparent electrodes 41 and 42disposed on both sides of the particle sheet 50 and connected to thepower source 30. The first electrode 41 is spread in a planar shape overone main surface of the particle sheet 50. The second electrode 42 isspread in a planar shape over the other main surface of the particlesheet 50. Moreover, like in FIG. 1, the shown screen 40 has a firstcover layer 46 that covers the first electrode 41 to form one outermostsurface of the screen 40 and a second cover layer 47 that covers thesecond electrode 42 to form the other outermost surface of the screen40.

Subsequently, the particle sheet 50 will be explained. As shown in FIG.11, the particle sheet 50 has a pair of base members 51 and 52, and aparticle layer 55 disposed between the pair of base members 51 and 52.The first base member 51 is joined to the first electrode 41. The secondbase member 52 is joined to the second electrode 42. The particle layer55 is sealed between the first base member 51 and the second base member52. The first base member 51 and the second base member 52 can be formedwith a material having strength to be able to seal the particle layer 55and having a function as a holder of the electrodes 41 and 42, and theparticle layer 55, which is, for example, a polyethylene terephthalateresin film. In the embodiment shown, the screen 40 is a reflective-typescreen 40 in which an image light beam passes through the first basemember 51. Therefore, the first base member 51 is transparent andpreferably has visible light transmittance at the same level as thefirst electrode 41 and the first cover layer 46.

Subsequently, the particle layer 55 will be explained. As shown well inFIG. 11, the particle layer 55 has a large number of particles 60 and aholder 56 for holding the particles 60. The holder 56 holds theparticles 60 so as to be operable. In the example shown, the holder 56has a large number of cavities 56 a. Each particle 60 is accommodated ineach cavity 56 a. The inner size of each cavity 56 a is larger than theouter size of the particle 60 in the cavity 56 a. Therefore, theparticle 60 is operable inside the cavity 56 a. The holder 56 swells bya solvent 57, like shown in FIG. 2. Since the holder 56 and the solvent57 are made of the same materials as those shown in FIG. 2, the detailedexplanation is omitted.

The particle 60 according to the second embodiment is typically asphere, provided with a first part 61 and a second part 62 havingdielectric constants different from each other. The first part 61 istransparent and disposed at the observer's side. The first part 61 andthe second part 62 are made contact with each other at a curvedinterface.

The volumes of the first part 61 and the second part 62 are differentfrom each other. FIG. 11 shows an example in which the volume of thefirst part 61 is larger than the volume of the second part 62. In thecase of FIG. 11, the second part 62 has a shape close to a sphere or anoval sphere. The surface of the second part 62, that is, the interfacewith the first part 61 is a convex surface. The particle 60 may notnecessarily be an ideal sphere. The second part 62 may also have a shapethat is a distorted version of the ideal sphere or oval sphere.

The first part 61 is a transparent member. As a specific material of thefirst part 61 is, for example, silicon oil and a transparent resinmaterial. The first part 61 is, ideally, disposed on the observer' sideas shown in FIG. 11. A light beam incident on the first part 61 passestherethough as it is and reaches the second part 62. The second part 62is different from the first part 61 in dielectric constant and has alight scattering or reflection function. Moreover, the second part 62 isconfigured to have a refractive index different from that of the firstpart 61. Furthermore, inside the second part 62, as shown in FIG. 12,diffused components 62 c, which diffuse a light beam, may be included.The diffused components 62 c change the travel direction of a light beamthat travels through the particle 60 by reflection, refraction, etc.Such a light diffusing function (light scattering function) of thediffused components 62 c is given by, for example, forming the diffusedcomponents 62 c by a material having a refractive index different fromthe material that constitutes the main part 62 c of the particle 60 orby a material capable of exerting a reflection operation to a lightbeam. As the diffused components 62 c having a refractive indexdifferent from the base material of the main part 62, resin beads, glassbeads, a metal compound, a porous material containing a gas, and merebabbles are listed up as examples.

As described above, the first part 61 and the second part are differentin optical characteristics. Moreover, the surface of the second part hasa convex surface shape. Accordingly, the light beam that has reached thesecond part 62 from the first part 61 is scattered or reflected in adirection in accordance with the convex surface shape of the surface ofthe second part 62. Therefore, a projected light beam from the projector20 is scattered or reflected by the second part 62 and then displayed onthe screen 40.

Since the surface of the second part has a convex surface shape, thelight beam that has passed the first part 61 to reach the surface of thesecond part 62 is scattered or reflected in a direction in accordancewith the convex surface curvature. A light beam incident on a convexsurface has a wider diffusion range than a light beam incident on aconcave surface. Therefore, in such a case of the present embodiment,when the second part 62 has a smaller volume than the first part 61 andthe surface of the second part 62 is a convex surface, it is possible towider the diffusion range of a light beam incident on each particle 60.

In the state where no voltage is applied to the first and secondelectrodes 41 and 42, the particles 60 in the particle layer 55 may beoriented in a variety of directions. In this case, by applying apredetermined initial voltage between the first and second electrodes,as shown in FIG. 11, it is possible to align the particles 60 so thatthe first part 61 of each particle 60 is oriented in the observer'sside. Or by adjusting specific gravity of the first part 61 and thesecond part 62, it is possible to align the particles 60 in thedirection shown in FIG. 11.

In the state of FIG. 11, when a voltage is applied between the first andsecond electrodes 41 and 42, an electric field is generated between thefirst and second electrodes 41 and 42, and because of this electricfield, an electron dipole moment is generated in each particle 60. Inthis occasion, the particle 60 operates toward a position at which avector of the electron dipole moment is oriented in a direct oppositedirection of a vector of the electric field. Therefore, when a voltageis applied between the first and second electrodes 41 and 42, and whenan electric field is generated in the particle sheet 50 located betweenthe first and second electrodes 41 and 42, the particles 60 operate inthe cavities 56 a in a posture stable to the electric field, that is, atthe position and orientation stable to the electric field. In the stateof FIG. 11, the second part 62 in each particle 60 is disposed to facethe plane direction of the particle layer 55. However, the posture ofthe particle 60 changes by varying the voltage between the first andsecond electrodes 41 and 42, and, accordingly, the surface orientationof the second part 62 changes with respect to the plane direction of theparticle layer 55. Since the second part 62 has a function of scatteringor reflecting a light beam incident on the first part 61, when thesurface orientation of the second part 62 changes, the incidence angleof a light beam incident on the surface of the second part 62 changes,the direction of scattering or reflection of the light beam on thesecond part 62 also changes. In this way, the diffusion characteristicsof the screen 40 can be changed.

Also in the present embodiment, it is desirable that the rotation angleof each particle 60 is less than 180 degrees. In other words, it isdesirable that, concerning the rotation angle of the particle 60, theparticle 60 rotates by an angle of less than ±90 degrees with theinitial posture of the particle 60 as a reference position. Accordingly,when the first part 61 faces the observer at the initial posture of theparticle 60, even though the particle 60 is rotated, at least part ofthe first part 61 faces the observer, so that a most part of the lightbeam incident on the screen 40 from the projector 20 passes through thefirst part 61 and is guided to the second part 62, to be scattered orreflected. Therefore, projected light intensity on the screen 40 can bemaintained at a high level.

The particles 60 each including the first part 61 and the second part 62different in dielectric constant can be produced by a variety of methodsincluding known techniques. The particles 60 can be produced by, forexample, a method to align spherical particles of organic or inorganicmatters in a single layer using an adhesive tape or the like, withdeposition of a resin component layer or of an inorganic matter layer,to be charged with positive and negative electricity, different fromsphere particles, on a hemisphere of each particle (a deposition method,for example, Japanese Patent Laid-Open No. S56-67887), a method using arotary disc (for example, Japanese Patent Laid-Open No. H6-226875), amethod to make contact two kinds of droplets different in dielectricconstant with each other in air by a splaying method or an ink jetmethod to form a single droplet (for example, Japanese Patent Laid-OpenNo. 2003-140204), and a microchannel production method proposed inJP2004-197083A. As proposed in JP2004-197083A, the first part 61 and thesecond part 62 different in dielectric constant from each other can beformed using materials different in charging characteristics from eachother.

When producing the particles 60 with the microchannel production method,by adjusting the speed, the joint direction, etc., in the case where twokinds of polymerizable resin components that constitute the continuousphase are joined to each other, and by adjusting the speed, thedischarge direction, etc., in the case where the continuous phase isdischarged into the spheroidizing phase, the outer shape of the obtainedparticles 60, the interface shape between the first part 61 and thesecond part 62 of each particle 60, etc. can be adjusted. In the exampleof the particle 60 shown in FIGS. 12 to 14, the volume of the first part61 is larger than the volume of the second part 62. Moreover, in theexample of the particle 60 shown in FIGS. 12 to 14, the interface atwhich the first part 61 and the second part 62 have surface contact witheach other is formed to be a concave surface when viewed from the firstpart 61 and a convex surface when viewed from the second part 62. Thesecond part 62 has a shape close to a sphere or an oval sphere.

Since the first part 61 of each particle 60 is transparent, the color ofthe second part 62 is viewed as the color of the particle 60. The colorof the second part 62 of the particle 60 can be adjusted by a coloringmaterial such as a pigment and a dye. As the pigment and the dye, avariety of known pigments and dyes can be used. As examples, pigmentsdisclosed in JP2005-99158A and JP2780723B, pigments or dyes disclosed inJP5463911B can be used.

Subsequently, an operation in displaying an image using this displayapparatus 10 will be explained. In the case of the particles 60 of FIG.11, since the second part 62 is smaller than the first part 61 and thesurface of the second part 62 is a convex surface, a light beam that haspassed the first part 61 and then reached the second part 62 isscattered or reflected, that is, diffused in a relatively wide areadepending on the convex surface curvature. Accordingly, the diffusionarea of the particles 60 of FIG. 11 becomes wider. Therefore, not onlyfor an observer situated just in front of the screen 40, but also for anobserver situated obliquely a little bit, a diffused light beam from thescreen 40 reaches, so that the viewing angle can be widened.

The screen 40 of the display apparatus 10 according to the presentembodiment can change the diffusion characteristics with time byapplying an alternating current voltage to the first and secondelectrodes 41 and 42 to rotate the particles 60. In more specifically,in the present embodiment, each particle 60 is rotated to change theorientation of the convex surface of the second part 62 of the particle60 with time with respect to the direction of an incident light beam. Inthis way, the diffusion characteristics of the screen 40 change withtime, and hence speckle patterns on the change with time. When thediffusion characteristics change with time at a sufficiently high speed,the speckle patterns are overlapped one another and averaged to beobserved by the observer. As a result, speckles become inconspicuous.

The shown screen 40 has the pair of electrodes 41 and 42. When a voltageis applied between the pair of electrodes 41 and 42, an electric fieldis formed in the particle sheet 50 located between the pair ofelectrodes 41 and 42. The particle layer 55 of the particle sheet 50holds the particles 60 so as to be operable, each including the firstpart 61 and the second part 62 different in dielectric constant. Sincethe particles 60 have been charged or when an electric field is formedin at least the particle layer 55, a dipole moment is generated, andhence the particles 60 operate in accordance with a vector of the formedelectric field. When the particles 60 operate, which have a function ofchanging a light travel direction, such as, a reflection function and adiffusion function, as shown in FIGS. 12 to 14, the diffusioncharacteristics of the screen 40 change with time. As a result, specklesbecome inconspicuous.

Concerning the difference in dielectric constant between the first part61 and the second part 62 of each particle 60, it is enough for thedielectric constants to be different to the extent that a specklereducing function can be exerted. Therefore, whether the dielectricconstants are different between the first part 61 and the second part 62of the particle 60 can be determined by whether the particle 60 held soas to be operable can operate in accordance with the change in electricfield vector.

The operating principle of the particles 60 to the holder 56 is tochange the orientation and position of each particle 60 so that theelectric charge or dipole moment of the particle 60 has a stablepositional relationship with an electric field vector. Therefore, when aconstant electric field is continuously applied to the particle layer55, the operation of the particle 60 stops after a certain period oftime. On the other hand, in order to make speckles inconspicuous, it isrequired that the operation of the particle 60 to the holder 56continues. Accordingly, the power source 30 applies a voltage so that anelectric field formed in the particle layer 55 varies with time. In theexample shown, the power source 30 applies an alternating currentvoltage between the pair of the first and second electrodes 41 and 42 soas to invert the vector of an electric field generated in the particlesheet 50. For example, in the example shown in FIG. 7, the power source30 repeatedly applies a voltage X[V] and a voltage −Y[V] to the pair ofthe first and second electrodes 41 and 42 of the screen 40. Togetherwith such application of an inverted electric field, as an example, theparticle 60 can repeatedly operate between the states of FIGS. 14 and 12with the state of FIG. 13 as a center state. The voltage to be appliedto the first and second electrodes 41 and 42 may not be limited to thatshown in FIG. 7, which may, for example, be an alternating currentvoltage or the like.

As described above, the particles 60 are accommodated in the cavities 56a formed in the holder 56. In the example shown in FIGS. 12 to 14, eachparticle 60 has an almost sphere outer shape. Each cavity 56 a thataccommodates the particle 60 has an almost sphere inner shape.Therefore, the particle 60 can perform rotational vibration about itscenter axis line, as shown by arrow lines in FIGS. 12 to 14. Dependingon the size of the cavity 56 a that accommodates the particle 60, theparticle 60 performs, not only the repeated rotational vibration, butalso translational motion. Moreover, the cavity 56 a is filled with thesolvent 57. The solvent 57 makes smooth the operation of the particle 60to the holder 56.

As described above, in the second embodiment, the particles 60 of theparticle layer 55 in the screen 40 are each configured to be a two-layerstructure of the first part 61 and the second part 62 that has a smallervolume than the first part 61. The first part 61 is transparent whilethe second part 62 has the light scattering or reflectingcharacteristics. A light beam that has passed through the first part 61to be incident on the interface with the second part 62 is diffused in awide area at the convex surface of the second part 62. In this way, notonly an observer situated just in front of the screen 40, but also anobserver situated in an oblique direction can view an image light beamdisplayed on the screen 40, so that the viewing angle can be widened.

The first part 61 and the second part 62 of the particles 60 in thepresent embodiment are different in dielectric constant from each other.Therefore, the particles 60 can be rotated by arranging the first part61 and the second part 62 on both sides of the particle layer 55 andapplying an alternating current voltage between the first part 61 andthe second part 62. Accordingly, the orientation of the convex surfaceof the second part 62 can be changed with time with respect to thedirection of a light beam that passes through the first part 61 to beincident on the second part 62. Since the second part 62 has the lightscattering or reflecting characteristics, the angle of scattering orreflection of the light beam incident on the second part 62 changes withtime, and hence speckles are hardly viewed.

In order to repeatedly rotate each particle 60, it is preferable thatits angle range is less than 180° as shown in FIGS. 12 to 14. In thiscase, the first part 61 can mainly be disposed at the observer's side.In other words, while a light beam is being radiated onto the screen 40,the first part 61 can be covered from the observer's side along thedirection of normal nd to screen 40. Therefore, it is possible to guidea light beam, which has passed through the first part 61, to the secondpart 62 to scatter or reflect the light beam at the second part 62.

Moreover, since the first part 61 of each particle 60 is transparent,the color of the particle 60 is decided by the color of the second part62. Therefore, even though the particle 60 performs rotary ortranslational motion, since the color of the second part 62 is alwaysviewed, the tone of the screen 40 does not change.

Third Embodiment

The example shown in the second embodiment is that the second part 62having a convex surface is provided in each particle 60 to widen thediffusing area. To the contrary, in the third embodiment, the shape ofthe second part 62 is changed to narrower the diffusing area.

FIGS. 15 to 18 are illustrations for explaining the third embodiment.FIG. 15 is a longitudinal sectional view of a screen 40. FIGS. 16 to 18are illustrations for explaining an operation of the screen 40 of FIG.15.

Particles 60 according to the third embodiment each have a first part 61and a second part 62 having a larger volume than the first part 61. Thematerials of the first part 61 and the second part 62 are the same asthose in the second embodiment. The first part 61 is a transparentmember while the second part 62 has the light scattering or reflectingfunction.

The interface between the first part 61 and the second part 62 is aconvex surface when viewed from the first part 61 and a concave surfacewhen viewed from the second part 62. A light beam incident on the secondpart 62 from the first part 61 travels in the direction of convergence.Accordingly, the screen 40 having the particles 60 according to thepresent embodiment can diffuse a light beam in a narrow area. Therefore,it is possible to collect diffused light beams in concentrated manner toan observer situated in a specific position in front of the screen 40.Viewing from this observer, it is possible to view the screen 40 at highcontrast.

As described, in the third embodiment, each particle 60 in the particlelayer 55 of the screen 40 narrows the diffusing area of an image lightbeam from the projector 20. Therefore, an observer situated in aspecific position can view a projected image on the screen 40 at highercontrast.

In the above-described first to third embodiments, although theexplanation has been made about the reflective-type screen 40, theseembodiments are also applicable to a transparent-type screen 40. In thecase of the transparent-type screen 40, it is required that a light beamfrom the projector 20 passes through the particles 60. Because of this,for example, the volume of the second part 62 may be made much smallerwith respect to the first part 61 to reduce the percentage of light thatpasses through the first part 61 to be incident on the second part 62.Or particles 60 having second parts 62 and particles 60 with no secondparts 62 may coexist. In the case of the transparent-type screen 40, itis desirable that the volume ratio of the first part 61 and the secondpart 62 in each particle 60 is adjusted so that light transmittancebecomes higher than light reflectance in the entire particle layer 55.

Fourth Embodiment

The screen according to the fourth embodiment is different in particles60 from the screens according to the above-described first to thirdembodiments. The particles 60 in the fourth embodiment are configured toshow higher reflectance to a light beam in the wavelength range of acoherent light beam oscillated by the coherent light source 21 than to alight beam outside the wavelength range of the coherent light beam.

Diffused components 66 b and 67 b, which are included in each particle60 according to the present embodiment, include a pigment thatselectively scatters a light beam in the wavelength range of a coherentlight beam oscillated by the coherent light source 21. Or a pigment or adye, which absorbs a light beam outside the wavelength range of thecoherent light beam oscillated by the coherent light source 21, may beadded to the main parts 66 a and 67 a of the particle 60. As the pigmentor dye, a color filter pigment disclosed in JP2780723B and a colorfilter dye disclosed in JP5463911B can be listed up as examples. Becauseof the pigment or dye, which absorbs a light beam outside the wavelengthrange of the coherent light beam, being added to the main parts 66 a and67 a of the particle 60, a light beam outside the wavelength range ofthe coherent light beam but in a wavelength of an ambient light beamsuch as an external light beam and an illumination light beam, is notscattered but absorbed in the particle 60. Accordingly, the effect ofthe ambient light beam to an image light beam is reduced to make itpossible to display a high contrast image. In this case, the diffusedcomponents 66 b and 67 b of the particle 60 may be configured with apigment that selectively scatters a light beam in the wavelength rangeof the coherent light beam oscillated by the coherent light source 21 ormay be configured with a material, such as resin beads, glass beads, ametal compound, a porous material containing a gas, and mere babbles,having a refractive index different from that of the materials thatconstitute the main parts 66 a and 67 a of the particle 60.

A conventional screen reflects an ambient light beam such as an externallight beam and an illumination light beam without distinguishing betweenthe ambient light beam and an image light beam. This results in a smalldifference in brightness between a part irradiated with the image lightbeam and a part not irradiated with the image light beam. Therefore, inorder to achieve high-contrast image display in the conventional screen,it is required to suppress the effect of an ambient light beam such asan external light beam and an illumination light beam using a means oran environment for making a room dark.

To the contrary, in the screen 40 of the display apparatus 10 in thepresent embodiment, the particles 60 included in the particle layer 55are configured to show higher reflectance to a light beam in thewavelength range of a coherent light beam oscillated by the coherentlight source 21 than to a light beam outside the wavelength range of thecoherent light beam. Therefore, it is restricted that a light beam of awavelength, which is outside the wavelength range of the coherent lightbeam but in a wavelength of an ambient light beam such as an externallight and an illumination light, is scattered on the screen 40.Accordingly, the effect of the ambient light beam to an image light beamcan be reduced, and hence a high-contrast image can be displayed even ina bright environment.

Moreover, according to the present embodiment, each particle 60 includedin the particle layer 55 is configured to show higher reflectance to alight beam in the wavelength range of a coherent light beam oscillatingfrom the coherent light source 21 than to a light beam outside thewavelength range of the coherent light beam. Therefore, it is restrictedthat a light beam of a wavelength, which is outside the wavelength rangeof the coherent light beam but in a wavelength of an ambient light beamsuch as an external light and an illumination light, is scattered on thescreen 40. Accordingly, the effect of the ambient light beam to an imagelight beam can be reduced, and hence a high-contrast image can bedisplayed even in a bright environment.

The example shown in the above-described embodiment is that the diffusedcomponents 66 b and 67 b included in the particle 60 are configured witha pigment that selectively scatters a light beam in the wavelength rangeof a coherent light beam oscillated by the coherent light source 21. Notto be limited to the example, for example, a pigment or a dye, whichabsorbs a light beam outside the wavelength range of the coherent lightbeam oscillated by the coherent light source 21, may be added to themain parts 66 a and 67 a of the particle 60. As the pigment or dye, acolor filter pigment disclosed in JP2780723B and a color filter dyedisclosed in JP5463911B can be listed up as examples. Because of thepigment or dye, which absorbs a light beam outside the wavelength rangeof the coherent light beam, being added to the main parts 66 b and 67 bof the particle 60, a light beam outside the wavelength range of thecoherent light beam, in a wavelength of an ambient light beam such as anexternal light beam and an illumination light beam, is not scattered butabsorbed in the particle 60. Accordingly, the effect of the ambientlight beam to an image light beam is reduced to make it possible todisplay a high contrast image. In this case, the diffused components 66b and 67 b of the particle 60 may be configured with a pigment thatselectively scatters a light beam in the wavelength range of thecoherent light beam oscillated by the coherent light source 21 or may beconfigured with a material, such as resin beads, glass beads, a metalcompound, a porous material containing a gas, and mere babbles, having arefractive index different from that of the materials that constitutethe main parts 66 b and 67 b of the particle 60.

Or a pigment or a dye, which absorbs a light beam outside the wavelengthrange of the coherent light beam, may be added to the holder 56 made ofsilicon rubber or the like. Moreover, as long as the function of thescreen 40 is not obstructed, a pigment or a dye, which absorbs a lightbeam outside the wavelength range of the coherent light beam, may beadded to the electrodes 41 and 42, the cover layers 46 and 47, the basemembers 51 and 52, and a layer of an adhesive or the like that joinsthese components, of the screen 40. Furthermore, a layer, having afunction of absorbing a light beam outside the wavelength range of thecoherent light beam oscillated by the coherent light source 21, may beprovided to the screen 40. By means of these examples, in the samemanner as in the case where a pigment or a dye, which absorbs a lightbeam outside the wavelength range of the coherent light beam, is addedto the main parts 66 a and 67 a of the particle 60, the effect of theambient light beam to an image light beam is reduced to make it possibleto display a high contrast image.

When the screen 40 is a reflective type, a layer, having a function ofabsorbing a light beam, which is outside the wavelength range of thecoherent light beam, from a light beam incident on the particle layer 55and a light beam reflected on the particle layer 55, is disposed on theobserver's side rather than on the particle layer 55's side.

To the contrary, when the screen 40 is a reflective type, a layer,having a function of absorbing a light beam outside the wavelength rangeof the coherent light beam, can be disposed at any position in thescreen 40, that is, between the particle layer 55 and the first basemember 51 or the second base member 52, between the first base member 51and the first electrode 41 or between the second base member 52 and thesecond electrode 42, and between the first electrode 41 and the firstcover layer 46 or between the second electrode 42 and the second coverlayer 47. However, from the point of view of restricting reflection ofan ambient light beam outside the wavelength range of the coherent lightbeam, it is preferable that the layer, having a function of absorbing alight beam outside the wavelength range of the coherent light beam, isdisposed at a position closer to the observer' side. In this case,improvement in contrast can be achieved more effectively.

The example shown in the above-mentioned embodiment is that the screen40 is a reflection-type screen. Not only limited to this example, asshown in FIG. 19, the screen 40 may be a transmission-type screen. Inthis case, each particle 60 included in the particle layer 55 isconfigured to show higher reflectance to a light beam in the wavelengthrange of a coherent light beam oscillated by the coherent light source21 than to a light beam outside the wavelength range of the coherentlight beam. Therefore, it is restricted that a light beam of awavelength, which is outside the wavelength range of the coherent lightbeam but in a wavelength of an ambient light beam such as an externallight and an illumination light, passes through the screen 40.Accordingly, an observer situated to face a surface of the screen 40opposite to the display-side surface 40 a can observe a high-contrastimage even in a bright environment. In the transmission-type screen 40,the second electrode 42, the second cover layer 47, and the second basemember 52 are configured to be transparent in the same manner as thefirst electrode 41, the first cover layer 46, and the first base member51, and preferably have the same visible light transmittance as theabove-described first electrode 41, first cover layer 46, and first basemember 51. Moreover, it is preferable that the quantities of thediffused components 66 b and 67 b added in the particle 60 are adjustedso that transmittance to a light beam incident on the particle 60 ishigher than reflectance to the light beam.

Fifth Embodiment

FIGS. 20 to 23 are illustrations for explaining a fifth embodiment ofthe present disclosure. A display apparatus 1 according to the fifthembodiment has the same configuration as that of FIG. 1. FIG. 20 is alongitudinal sectional view of a screen 40 according to the fifthembodiment. FIGS. 21 to 23 are illustrations for explaining an operationof the screen 40 of FIG. 1.

The display apparatus 10 according to the fifth embodiment, like shownin FIG. 1, has a projector 20 and a screen 40 to be irradiated with animage light beam from the projector 20. As shown in FIG. 20, the screen40 has a particle sheet 50 having a plurality of particles, andtransparent electrodes 41 and 42 connected to the power source 30 anddisposed on both sides of the particle sheet 50.

The particle sheet 50 has a pair of base members 51 and 52, and aparticle layer 55 disposed between the pair of base members 51 and 52.The particle layer 55 has a large number of particles 60 and a holder 56for holding the particles 60. The holder 56 holds the particles 60 so asto be operable. The particles 60 have a function of changing the traveldirection of an image light beam projected from the projector 20. In theexample shown, the particles 60 have a function of diffusing the imagelight beam by diffuse reflection.

The particles 60 each have a three-layer structure in which a first part61, a third part 63, and a second part 62 are aligned in this order,among which the first part 61 is disposed on the observer's side. Thethird part 63 is in surface contact with the first part 61, to controlan incident light beam from the first part 61. The second part 62 is insurface contact with a second face 63 b of the third part 63, which isopposite to a first face 63 a of the third part 63, which is in surfacecontact with the first part 61, the second part 62 being different indielectric constant from the first part 61. The third part 63 issandwiched between the first part 61 and the second part 62, to be insurface contact with the first part 61 and with the second part 62.

The first part 61 and the second part 62 are transparent members. Thethird part 63 has a function of scattering or reflecting a light beamincident on the first part 61. The third part 63 is configured to have arefractive index different from that of the first part 61. Furthermore,inside the third part 63, diffused components 63 c for diffusing a lightbeam may be included. These diffused components 63 c change the traveldirection of a light beam that travels through the particle 60 byreflection, refraction, etc. Such a light diffusing function (lightscattering function) of the diffused components 63 c is given by, forexample, forming the diffused components 63 c with a material having arefractive index different from that of the material that constitutesthe main part 63 c of the particle 60 or with a material capable ofexerting a reflection operation to a light beam. As the diffusedcomponents 63 c having a refractive index different from that of thebase material of the main part 63, resin beads, glass beads, a metalcompound, a porous material containing a gas, and mere babbles arelisted up as examples.

The particle 60 is typically a sphere, in which a thin layer passingthrough its center area is the third part 63, with the first part 61 andthe second part 62 made in surface contact on both sides (the first face63 a and the second face 63 b) of the third part 63. The particle 60 maynot necessarily be an ideal sphere. Therefore, the shapes of the firstpart 61, the third part 63, and the second part 62 change depending onthe shape of the particle 60.

The thickness between the first face 63 a and the second face 63 b ofthe third part 63 of the particle 60 is thinner than a maximum thicknessof the first face 63 a of the first part 61 in the direction of normalto the first face 63 a. The thickness between the first face 63 a andthe second face 63 b of the third part 63 of the particle 60 is thinnerthan a maximum thickness of the second face 63 b of the third part 63 inthe direction of normal to the second face 63 b. The first face 63 a andthe second face 63 b have, for example, a circular shape or an ovalshape and the third part 63 has, for example, a circular, oval,cylindrical or elliptic cylindrical shape.

In an initial state where no voltage is applied to the first and secondelectrodes 41 and 42, the plane direction of the third part 63 isoriented almost parallel to the plane direction of the particle layer55. In the initial state, the plane direction of the third part 63 canbe oriented almost parallel to the plane direction of the particle layer55, for example, by adjusting the specific gravity of the first part 61,the second part 62, and the third part 63 of each particle 60. Or theplane direction of the third part 63 may be oriented almost parallel tothe plane direction of the particle layer 55, for example, by applying apredetermined initial voltage to the first and second electrodes 41 and42 in the initial state.

When a voltage is applied between the first and second electrodes 41 and42, an electric field is generated between the first and secondelectrodes 41 and 42, and because of this electric field, an electrondipole moment is generated in each particle 60. In this occasion, theparticle 60 operates toward a position at which a vector of the electrondipole moment is oriented in the direct opposite direction of a vectorof the electric field. Therefore, when a voltage is applied between thefirst and second electrodes 41 and 42, and an electric field isgenerated in the particle sheet 50 located between the first and secondelectrodes 41 and 42, the particles 60 operate in the cavities 56 a in aposture stable to the electric field, that is, at the position andorientation stable to the electric field. The posture of each particle60 changes by varying the voltage between the first and secondelectrodes 41 and 42, and, accordingly, the angle of the surfaceorientation of the third part 63 changes with respect to the planedirection of the particle layer 55. Since the third part 63 has afunction of scattering or reflecting a light beam incident on the firstpart 61, when the angle of the third part 63 changes, the diffusioncharacteristics of the screen 40 can be changed.

It is desirable that the rotation angle of each particle 60 is less than180 degrees. In other words, it is desirable that, concerning therotation angle of the particle 60, the particle 60 rotates by an angleof less than ±90 degrees with the initial posture of the particle 60 asa reference position. Accordingly, when the first part 61 faces theobserver at the initial posture of the particle 60, even though theparticle 60 is rotated, at least part of the first part 61 faces theobserver, so that a most part of the light beam incident on the screen40 from the projector passes through the first part 61 and is guided tothe third part 63, to be scattered or reflected. Therefore, projectedlight intensity on the screen 40 can be maintained at a high level.

The particles 60 each including the first part 61, the third part 63,and the second part 62 different in dielectric constant can be producedby a variety of methods including known techniques. The particles 60 canbe produced by, for example, a method to align spherical particles oforganic or inorganic matters in a single layer using an adhesive tape orthe like, with deposition of a resin component layer or of an inorganicmatter layer, to be charged with positive and negative electricity,different from sphere particles, on a hemisphere of each particle (adeposition method, for example, Japanese Patent Laid-Open No.S56-67887), a method using a rotary disc (for example, Japanese PatentLaid-Open No. H6-226875), a method to make two kinds of droplets ofdifferent dielectric constants in contact with each other in air by asplaying method or an ink jet method to from a single droplet (forexample, Japanese Patent Laid-Open No. 2003-140204), and a microchannelproduction method proposed in JP2004-197083A. As proposed inJP2004-197083A, the first part 61, the second part 62, and the thirdpart 63 different in dielectric constant from one another can be formedwith materials different in charging characteristics from one another.The third part 63 can be formed using a scattering material or lightreflection flakes. A light reflection flame is formed by, for example,mixing flakes into which a reflection material is finely crushed, into abase material of the third part 63.

The microchannel production method is to use a continuous phase and aspheroidizing phase having an oily/aqueous (O/W type) or aqueous/oily(W/O type) relationship and to sequentially discharge a continuous phaseincluding materials corresponding to the first part 61, the second part62, and the third part 63 from a first microchannel, through which thecontinuous phase is transferred, into the spheroidizing phase of a fluidmedium which flows through a second microchannel, thereby producingbipolar particles 60 that are three-layer polymer particles 60 and havepolarities of (±) in charge.

When producing the particles 60 with the microchannel production method,by adjusting the speed, the joint direction, etc., in the case where thethree kinds of polymerizable resin components that constitute thecontinuous phase are joined to each other, and by adjusting the speed,the discharge direction, etc., in the case where the continuous phase isdischarged into the spheroidizing phase, the outer shape of the obtainedparticles 60, the interface shape between the first part 61, the secondpart 62, and the third part 63 of each particle 60, etc. can beadjusted. In the example of the particle 60 shown in FIGS. 21 to 23, thevolume ratio of the first part 61 and the volume ratio of the secondpart 62 are the same as each other. Moreover, in the example of theparticle 60 shown in FIGS. 21 to 23, the first face 63 a on which thefirst part 61 and the second part 62 are made in surface contact witheach other and the second face 63 b on which the third part 63 and thesecond part 62 are made in surface contact with each other are formedinto a circular or oval shape. And the particle 60 shown in FIGS. 21 to23 is a sphere. That is, in the particle 60 shown in FIGS. 21 to 23, thefirst part 61 and the second part 62 are each a hemisphere and the thirdpart 63 is disc like. However, as described above, the third part 63 mayhave a few thickness and the shape of the particle 60 may not be anideal sphere.

Since the first part 61 and the second part 62 of each particle 60 istransparent, the color of the third part 63 is viewed as the color ofthe particle 60. The color of the third part 63 of the article 60 can beadjusted by a coloring material such as a pigment and a dye. As thepigment and the dye, a variety of known pigments and dyes can be used.As examples, pigments disclosed in JP2005-99158A and JP2780723B,pigments or dyes disclosed in JP5463911B can be used.

Subsequently, an operation in displaying an image using this displayapparatus 10 will be explained.

A light beam projected onto the screen 40 passes through the first coverlayer 46 and the first electrode 41, and then reaches the particle sheet50. The light beam is reflected on the third part 63 of the particle 60of the particle sheet 50 by diffuse reflection and emitted towardseveral directions in the observer's side of the screen 40. Therefore,at respective points in the observer's side of the screen 40, reflectedlight beams from respective points on the screen 40 can be observed. Asa result, an image corresponding to an area irradiated with the coherentlight beams on the screen 40 can be observed.

The light source 21 may include a plurality of light sources that emitcoherent light beams of wavelengths different from one another. In thecase, the controller 35 controls a light source corresponding to a lightbeam of each wavelength independently from the other light sources. As aresult, it is possible to display an color image on the screen 40.

The screen 40 of the display apparatus 10 according to the presentembodiment changes the diffusion characteristics with time by rotatingthe particles 60. In more detail, in the present embodiment, theinclination angle of the third part 63 of each particle 60 to thedirection of an incident light is changed with time. Accordingly, thediffusion characteristics of the screen 40 change with time, so thatspeckle patterns on the screen 40 change with time. When the diffusioncharacteristics change with time at a sufficiently high speed, thespeckle patterns are overlapped one another and averaged to be observedby the observer. As a result, speckles become inconspicuous.

The shown screen 40 has a pair of electrodes 41 and 42. When a voltageis applied between the pair of electrodes 41 and 42, an electric fieldis formed in the particle sheet 50 located between the pair ofelectrodes 41 and 42. The particle layer 55 of the particle sheet 50holds the particles 60 so as to be operable, each including the firstpart 61 and the second part 62 different in dielectric constant. Sincethe particles 60 have been charged or when an electric field is formedin at least the particle layer 55, a dipole moment is generated, andhence the particles 60 operate in accordance with a vector of the formedthe electric field. When the particles 60 operate, which have a functionof changing a light travel direction, such as, a reflection function anda diffusion function, as shown in FIGS. 21 to 23, the diffusioncharacteristics of the screen 40 change with time. As a result, specklesbecome inconspicuous.

Concerning the difference in dielectric constants between the first part61 and the second part 62 of each particle 60, it is enough for thedielectric constants to be different to the extent that a specklereducing function can be exerted. Therefore, whether the dielectricconstants between the first part 61 and the second part 62 of theparticle 60 are different from each other can be determined by whetherthe particle 60 held so as to be operable can operate in accordance withthe change in electric field vector.

The operating principle of the particles 60 to the holder 56 is tochange the orientation and position of each particle 60 so that theelectric charge or dipole moment of the particle 60 has a stablepositional relationship with an electric field vector. Therefore, when aconstant electric field is continuously applied to the particle layer55, the operation of the particle 60 stops after a certain period oftime. On the other hand, in order to make speckles inconspicuous, it isrequired that the operation of the particle 60 to the holder 56continues. Accordingly, the power source 30 applies a voltage so that anelectric field formed in the particle layer 55 varies with time. In theexample shown, the power source 30 applies an alternating currentvoltage between the pair of electrodes 41 and 42 so as to invert thevector of an electric field generated in the particle sheet 50. Forexample, in the example shown in FIG. 7, the power source 30 repeatedlyapplies a voltage X[V] and a voltage −Y[V] to the pair of electrodes 41and 42. Together with such application of an inverted electric field, asan example, the particle 60 can repeatedly operate between the states ofFIGS. 23 and 21 with the state of FIG. 22 as a center state. The voltageto be applied to the first and second electrodes 41 and 42 may not belimited to that shown in FIG. 7, which may, for example, be analternating current voltage or the like.

As described above, the particles 60 are accommodated in the cavities 56a formed in the holder 56. In the example shown in FIGS. 21 to 23, eachparticle 60 has an almost sphere outer shape. Each cavity 56 a thataccommodates the particle 60 has an almost sphere inner shape.Therefore, the particle 60 can perform rotational vibration about arotation axis line passing its center, as shown by an arrow line inFIGS. 21 to 23. Depending on the size of the cavity 56 a thataccommodates the particle 60, the particle 60 performs, not only therepeated rotational vibration, but also translational motion. Moreover,the cavity 56 a is filled with the solvent 57. The solvent 57 makessmooth the operation of the particle 60 to the holder 56.

As described above, in the fifth embodiment, the particles 60 of theparticle layer 55 in the screen 40 each have a three-layer structure ofthe first part 61, the second part 62, and the third part 63. The firstpart 61 and the second part 62 are transparent and different indielectric constant from each other. The third part 63 is disposedbetween the first part 61 and the second part 62, having a lightscattering or reflecting function. Since the first part 61 and thesecond part 62 of each particle 60 are transparent, the color of theparticle 60 is decided by the color of the third part 63. Therefore,even though the particle 60 performs rotary or translational motion, thecolor of the particle 60 does not change and hence the color of thescreen 40 does not change. Since the third part 63 has the lightscattering or reflecting function, a light beam incident on the firstpart 61 of the particle 60 can be scattered or reflected by the thirdpart 63.

On both sides of the particle layer 55 including such particles 60, whenthe first and second electrodes 41 and 42 are arranged and analternating current voltage is applied therebetween, the inclinationangle of the third part 63 in the plane direction with respect to thedirection of an incident light can be changed with time. Since the thirdpart 63 has the light scattering or reflecting function, the scatteringor reflecting angle of a light beam incident on the third part 63changes with time and hence speckles become inconspicuous.

Furthermore, according to the present embodiment, while a light beam isbeing radiated onto the screen 40, the particles 60 can be repeatedlyrotated in the particle layer 55. In other words, the particles 60 canoperate to effectively change the diffusion characteristics in anextremely small space. Therefore, by repeatedly rotating the particles60, while realizing a thin particle layer 55 and a thin screen 40,speckles can effectively be made inconspicuous. When repeatedly rotatingeach particle 60, its angular range is preferably less than 180° asshown in FIGS. 21 to 23. In this case, the first part 61 and the thirdpart 63 can mainly be situated on the observer's side. In other words,while a light beam is being radiated onto the screen 40, it is possiblethat the first part 61 covers the third part 63 when viewed from theobserver's side along the direction of normal nd to the screen 40.Accordingly, it is possible to guide a light beam that has passed thefirst part 61 to the third part 63 to scatter or reflect the light beamat the third part 63.

Sixth Embodiment

The example explained in the fifth embodiment is about thereflective-type screen 40, while an example shown in the sixthembodiment is about an application to a transparent-type screen 40.

FIG. 24 is a longitudinal sectional view of a screen 40 according to thesixth embodiment. The screen 40 according to the sixth embodiment is atransparent type. The screen 40 of FIG. 24 is different from the screen40 of FIG. 20 in orientation of the particles 60 in the particle layer55. The particles 60 according to the sixth embodiment have athree-layer structure of the first part 61, the second part 62 and thethird part 63, like the fifth embodiment, the material of each partbeing the same as that in the fifth embodiment.

The particles 60 of FIG. 24 have a reference posture, which correspondsto the posture of the particles 60 of FIG. 20 rotated by 90 degrees, andare capable of rotating by 90 degrees in both directions from thereference posture. In order to rotate the particles 60 of FIG. 24, it isrequired to apply an electric field in the particle layer 55 in adirection different from the direction in FIG. 20 by 90 degrees.Accordingly, in the present embodiment, first electrodes 41 and secondelectrodes 42 are alternately arranged in a stripe pattern only on oneside opposite to the observer and an electric field is formed in theplane direction of the particle layer 55 by the electrodes 41 and 42,that is, in a direction different from the direction in FIG. 20 by 90degrees. In more specifically, in the present embodiment, an alternatingcurrent voltage is applied between the first electrode 41 and the secondelectrode 42 adjacent to each other to cyclically switch the electricfield formed in the plane direction of the particle layer 55. In thisway, the particles 60 situated in the vicinity of the associated firstelectrode 41 and second electrode 42 rotate in accordance with thefrequency of the alternating current voltage.

The screen 40 of FIG. 24 is in the initial state where no voltage isapplied to the first electrode 41 and the second electrode 42, so thatthe plane direction of the third part 63 of each particle 60 in theparticle layer 55 is oriented almost parallel to the direction of normalto the particle layer 55. Since the third part 63 is very thin, the mostpart of a light beam incident on the screen 40 pass through the firstpart 61 and the second part 62 of each particle 60. Therefore, anobserver situated to face a surface of the screen 40, opposite to thesurface thereof on which a light beam from the projector 20 is incident,can view a projected light beam from the projector 20.

In the initial state where no voltage is applied to the first electrode41 and the second electrode 42, in order to orient the plane directionof the third part 63 parallel to the direction of normal to the particlelayer 55, it can be considered to adjust the specific gravity of thefirst part 61, the second part 62, and the third part 63 in the particle60. Or a predetermined initial voltage may be applied between the firstelectrode and the second electrode to orient the plane direction of thethird part 63 of each particle 60 in the direction of normal to theparticle layer 55.

When an alternating current voltage is applied to the first electrode 41and the second electrode 42, the particles 60 rotate, so that theinclination angle of the third part 63 of the particle 60 to thedirection of an incident light changes with time. Therefore, thedirection of a light beam scattered or reflected by the third part 63changes with time and hence speckles are hardly viewed.

As described above, in the sixth embodiment, the transparent-type screen40 can be realized by setting the state of the particles 60, which arerotated in a direction different from that of the fifth embodiment by 90degrees, to the reference posture of the particles 60. Moreover, byrotating each particle 60 within a range less than 180 degrees from thereference posture, speckles on the screen 40 become inconspicuous.

Seventh Embodiment

The examples explained in the first to sixth embodiments are aboutapplications to the reflective- or transmission-type screen 40, while anexample shown in the seventh embodiment is about an application to alight control sheet such as a window and a lighting film.

FIG. 25 is a longitudinal sectional view of a light control sheet 75according to the seventh embodiment. The light control sheet 75 of FIG.25 can be used as a lighting sheet to improve lighting efficiency.

The light control sheet 75 of FIG. 25 is provided with a light controllayer 71, an adhesive layer 72 disposed at one surface of the lightcontrol layer 71, and a protective film 73 disposed at the other surfaceof the light control layer 71. The light control sheet 75 of FIG. 25 canbe layered on a lighting member 74 such as a window with the adhesivelayer 72 interposed therebetween. Or the light control sheet 75according to the present embodiment may be formed integrally inside thelighting member 74 such as a window.

If the adhesive layer 72 is left exposed, the light control sheet 75 isadhered to an unexpected object, so that before adhering the lightcontrol sheet 75 to the lighting member 74 such as a window, a peel-offfilm not shown may be attached to the adhesive layer 72. The peel-offfilm is peeled off before adhering the light control sheet 75 to thelighting member 74. The protective film 74 is peeled off after the lightcontrol sheet 75 is adhered to the lighting member 74. Hereinafter, thepeel-off film and the protective film 73 may each be referred to simplyas a “layer”.

Compositions of the adhesive layer 72 are, for example, one or morekinds of thermoplastic resin from polyvinyl acetal resin,ethylene-vinylacetate copolymer resin, ethylene-acrylate copolymerresin, polyurethane resin, and polyvinyl alcohol resins, which are mixedwith an additive such as a plasticizer, an antioxidant, and anultraviolet ray shielding agent, or formed by mixing an acrylic-resinadhesive, a crosslinking agent, and a diluent.

The light control layer 71 has a pair of base member layers 51 and 52, aparticle layer 55 provided between the base member layers, and first andsecond electrodes 41 and 42 provided at the base member layer 52's side.The particle layer 55 has the same configuration as that of FIG. 20,including a plurality of particles 60. In the same manner as in FIGS. 20and 24, each particle 60 has a first part 61, a second part 62, and athird part 63. It is also the same as in FIGS. 20 and 24 that the firstpart 61 and the second part 62 are transparent and the third part 63 hasthe light scattering or reflecting function.

In the same manner as in the sixth embodiment, the first and secondelectrodes 41 and 42 are alternately arranged in a stripe pattern. Byapplying a predetermined voltage between the adjacent first and secondelectrodes 41 and 42, an electric field can be formed betweencorresponding the first and second electrodes 41 and 42 in the planedirection of the particle layer 55.

Since no laser light beam is radiated in the seventh embodiment, so thatit is not required to make speckles inconspicuous, the voltage to beapplied between the first and second electrodes 41 and 42 may be adirect current voltage.

The plane direction of the third part 63 is oriented in a directionoblique to the layered direction of the light control layer 71.Accordingly, when a light beam, which is incident on a surface of thelight control layer 71 on the lighting member 74's side, is incident onthe third part 63, it is possible that the light beam bounces offobliquely upward. Therefore, when the light control sheet 75 of FIG. 25is attached to a window extending in the vertical direction, it ispossible that external light incident from the window bounces off in aceiling direction in a room, so that it is possible to illuminate theroom brightly in the ceiling direction utilizing natural light.

In order to orient the plane direction of the third part 63 of eachparticle 60 in the particle layer 55 oblique to the layered direction ofthe light control layer 71 as shown in FIG. 25, it can be considered toapply a predetermined initial voltage between the adjacent first andsecond electrodes 41 and 42. In the case where the plane direction ofthe third part 63 can be oriented oblique to the layered direction ofthe light control layer 71 by adjusting the specific gravity of thefirst part 61, the second part 62, and the third part 63 in eachparticle 60 without voltage application, the electrodes may be omitted.Accordingly, in the present embodiment, the electrodes may not always benecessary components.

However, depending on the season or time zone, if it is desired toadjust the oblique angle of the third part 63 of each particle 60, thefirst and second electrodes 41 and 42 are necessary components.Depending on the sunlight incidence angle, by adjusting the voltage tobe applied to the first and second electrodes 41 and 42, at least one ofthe functions on antiglare, lighting, and privacy in the room can beachieved.

As described above, in the seventh embodiment, since, the particle layer55 including the particles 60 each having the first part 61, the secondpart 62, and the third part 63 is installed in the light control sheet75. Therefore, the light control sheet 75 excellent in at least one ofthe antiglare, lighting, and privacy can be realized.

A variety of modifications can be added to the above-described fifth toseventh embodiments. One example of the modification will be explainedwith reference to the drawings. In the following explanation and thedrawings to be used in the following explanation, for the elements to beconfigured in the same manner as those in the above-describedembodiments, the same signs as those used for the corresponding elementsin the above-described embodiments are used and the duplicateexplanation is omitted.

In the example described above, the first part 61 and the second part 62in each particle 60 are almost the same in volume and the third part 63is disposed at almost the center area of the particle 60. However, thefirst part 61 and the second part 62 may be different in volume. In FIG.26, the first part 61 has a larger volume than the second part 62 andthe third part 63 is disposed apart from the center of the particle 60.Conversely to FIG. 26, the first part 61 has a smaller volume than thesecond part 62.

When the particles 60 are produced by the above-described microchannelproduction method, the first part 61 and the third part 63 may bedifferent in volume depending on the particles 60, so that the particles60 of FIGS. 20 and 26 may coexist. Even in such a case, the particles 60rotate in the same manner by means of an alternating current voltageapplied to the first and second electrodes, and hence there is noparticular practical problem.

In the present embodiment, it is a precondition that the first part 61is disposed at the observer's side not at the second part 62's side.Therefore, it is desirable for the first part 61 to take in a light beamfrom the projector 20 with no losses and guide it to the third part 63.To the contrary, the second part 62 may have the light absorbingfunction. The light absorbing function of the second part 62 can bedeveloped when, as an example, the second part 62 includes alight-absorbing coloring material, specifically, a pigment such ascarbon black and titan black. When the second part 62 has the lightabsorbing function, a light beam Lc, incident from a direction differentfrom the direction of an image light beam La from the projector 20, canbe absorbed by the second part 62. The light beam to be absorbed by thethird part 63 may, for example, be an ambient light beam from anillumination apparatus 90 (refer to FIG. 1) present in the place wherethe display apparatus 10 is installed. By selecting and absorbing thelight beam Lc except for the image light beam La incident on the screen40, without loosing the brightness of a displayed image, it is possibleto efficiently improve the contrast of the displayed image.

Eighth Embodiment

A display apparatus 10 according to the eighth embodiment is providedwith a transparent-type screen 40. The entire configuration of thedisplay apparatus 10 is, for example, the same as that of FIG. 19. Thelongitudinal sectional view of the transparent-type screen 40 is, forexample, the same as FIG. 2. FIGS. 27 to 29 are illustrations forexplaining an operation of the transparent-type screen. A voltagewaveform to be applied from the power source 30 to the transparent-typescreen 40 is, for example, represented by a graph such as shown in FIG.7.

A transparent-type display apparatus 10 according to the presentembodiment has a projector 20 and a transparent-type screen 40 to beirradiated with an image light beam from the projector 20. As describedlater, the transparent-type screen 40 is capable of changing with timethe diffusion characteristics that affect an incident light beam.Accordingly, speckles become inconspicuous. In relation to such functionof the transparent-type screen 40, the transparent-type displayapparatus 10 further has a power source 30 and a controller 35. Thepower source 30 applies a voltage to the transparent-type screen 40. Thecontroller 35 adjusts the applied voltage from the power source 30 tocontrol a mode of the transparent-type screen 40. Moreover, thecontroller 35 controls an operation of the projector 20. As an example,the controller 35 is a general-purpose computer.

For example as shown in FIG. 3, the projector 20 projects a coherentlight beam onto the transparent-type screen 40 so as to scan the entirearea of the transparent-type screen 40. Scanning is performed at highspeeds. In accordance with an image to be formed, the projector 20 stopsemission of the coherent light beam from the coherent light source 21.In other words, the coherent light beam is projected onto only aposition on the transparent-type screen 40 at which the image is to beformed. As a result, the image is formed on the transparent-type screen40. The operation of the projector 20 is controlled by the controller35.

The transparent-type screen 40 according to the present embodiment has aparticle sheet 50 having a plurality of particles, and electrodes 41 and42 connected to the power source 30. The particle sheet 50 has a pair ofbase members 51 and 52, and a particle layer 55 disposed between thepair of base members 51 and 52. The particle layer 55 has a large numberof particles 60 and a holder 56 for holding the particles 60. Theparticles 60 have a function of changing the travel direction of animage light beam projected from the projector 20. In the example shown,the particles 60 have a function of diffusing the image light beam,especially, by diffuse transmission.

Each particle 60 includes a first part 61 and a second part 62 differentin dielectric constant. When this particle 60 is placed in an electricfield, an electron dipole moment is generated in the particle 60. Inthis occasion, the particle 60 operates in such a manner that a vectorof the electron dipole moment is oriented in a complete oppositedirection of a vector of the electric field. Therefore, when a voltageis applied between the first electrode 41 and the second electrode 42 sothat an electric field is generated in the particle sheet 50 locatedbetween the first electrode 41 and the second electrode 42, the particle60 operates in each cavity 56 a in such a manner that the particle 60takes a stable posture with respect to the electric field, that is, astable position and orientation with respect to the electric field. Thetransparent-type screen 40 changes its diffusion characteristics inaccordance with the operation of the particles 60 having the lightdiffusion function. The first part 61 and the second part 62 aretransparent. It is preferable that the first part 61 and the second part62 have the same visible light transmittance as the above-describedfirst electrode 41 and the like.

When producing the particles 60 with the microchannel production method,by adjusting the speed, the joint direction, etc., in the case where thetwo kinds of polymerizable resin components that constitute thecontinuous phase are joined to each other, and by adjusting the speed,the discharge direction, etc., in the case where the continuous phase isdischarged into the spheroidizing phase, the outer shape of the obtainedparticles 60, the interface shape between the first part 61 and thesecond part 62 of each particle 60, etc. can be adjusted. In the exampleof the particle 60 shown in FIGS. 27 to 29, the volume ratio of thefirst part 61 and the volume ratio of the second part 62 are the same aseach other. Moreover, in the example of the particle 60 shown in FIGS.27 to 29, the interface between the first part 61 and the second part 62is formed into a planar shape. And the particle 60 shown in FIGS. 27 to29 is a sphere. That is, in the particle 60 shown in FIGS. 27 to 29, thefirst part 61 and the second part 62 are each a hemisphere.

When two kinds of polymerizable resin components that constitute thecontinuous phase include diffused components, the first part 61 and thesecond part 62 of the particle 60 can be given an internal diffusionfunction. In the example shown in FIGS. 27 to 29, the first part 61 ofthe particle 60 has a first main part 66 a and a plurality of firstdiffused components (diffused particles) 66 b diffused in the first mainpart 66 a. In the same manner, the second part 62 has a second main part67 a and a plurality of second diffused components (diffused particles)67 b diffused in the second main part 67 a. In other words, the sphereparticle 60 shown in FIGS. 27 to 29 is capable of giving a diffusionfunction to a light beam propagating inside the first part 61 and alight beam propagating inside the second part 62. Here, the diffusedcomponents 66 b and 67 b are components capable of exerting an action tochange the travel direction of a light beam travelling inside theparticle 60 by reflection, refraction, etc. Such light diffusionfunction (light scattering function) of the diffused components 66 b and67 b is given by, for example, forming the diffused components 66 b and67 b by materials having a refractive index different from those of thematerials that constitute the main parts 66 a and 67 a of the particle60 or by materials capable of exerting a reflection operation to a lightbeam. As the diffused components 66 b and 67 b having a refractive indexdifferent from those of the materials that constitute the main parts 66a and 67 a, resin beads, glass beads, a metal compound, a porousmaterial containing a gas, and mere babbles are listed up as examples.It is preferable that the quantities of the diffused components 66 b and67 b added in the particle 60 are adjusted so that transmittance to alight beam incident on the particle 60 is higher than reflectance to thelight beam incident on the particle 60.

The particle layer 55, the particle sheet 50, and the transparent-typescreen 40 can be produced as described below as an example.

The particle layer 55 can be produced by a production method disclosedin JP1-28259A. That is, first of all, an ink in which the particles 60are dispersed in polymerizable silicon rubber is prepared. Then, the inkis stretched by a coater or the like and polymerized further by heatingor the like to be formed into a sheet. By these steps, the holder 56that holds the particles 60 is obtained. Subsequently, the holder 56 isdipped into the solvent 57 such as silicon oil for a certain period oftime. When the holder 56 swells, a gap filled with the solvent 57 isformed between the holder 56 made of silicon rubber and each particle60. As a result, the cavities 56 a that accommodate the solvent 57 andthe particles 60 are defined. As described above, the particle layer 55can be produced.

Subsequently, by a production method disclosed in JP2011-112792A, thetransparent-type screen 40 can be produced using the particle layer 55.First of all, the particle layer 55 is covered with the pair of basemembers 51 and 52, and sealed by lamination or using an adhesive or thelike. In this way, the particle sheet 50 is produced. Subsequently, thefirst electrode 41 and the second electrode 42 are disposed on theparticle sheet 50, and furthermore, the first cover layer 46 and thesecond cover layer 47 are disposed thereon, and then the Fresnel lenslayer 70 is disposed thereon to obtain the transparent-type screen 40.

Subsequently, an operation in displaying an image using thistransparent-type display apparatus 10 will be explained.

First of all, under control by the controller 35, the coherent lightsource 21 of the projector 20 oscillates a coherent light beam. Thelight beam from the projector 20 is subjected to optical pathadjustments by a scanning device not shown and radiated onto thetransparent-type screen 40. As shown in FIG. 3, the scanning device notshown adjusts the optical path of the light beam so that the light beamscans the display-side surface 40 a of the transparent-type screen 40.Emission of the coherent light beam by the coherent light source 21 iscontrolled by the controller 35. In accordance with an image to bedisplayed on the transparent-type screen 40, the controller 35 stops theemission of the coherent light beam from the coherent light source 21.The operation of the scanning device included in the projector 20 isperformed at such a high speed that it cannot be resolved by human eyes.Therefore, the observer observes simultaneously light beams radiated ata given time interval on respective points on the transparent-typescreen 40.

A light beam projected onto the transparent-type screen 40, after beingdeflected by the Fresnel lens layer 70 to be an almost parallel lightbeam, passes through the first cover layer 46 and the first electrode41, and then reaches the particle sheet 50. The light beam is diffusedby the particles 60 of the particle sheet 50 and passes the particles60, and then is emitted toward several directions in the observer's sideof the transparent-type screen 40. Therefore, at respective points inthe observer's side of the transparent-type screen 40, transmitted lightbeams from respective points on the transparent-type screen 40 can beobserved. As a result, an image corresponding to an area irradiated withthe coherent light beams on the transparent-type screen 40 can beobserved.

The coherent light source 21 may include a plurality of light sourcesthat emit coherent light beams of wavelengths different from oneanother. In the case, the controller 35 controls a light sourcecorresponding to a light beam of each wavelength independently from theother light sources. As a result, it is possible to display a colorimage on the transparent-type screen 40.

When a coherent light beam is used to form an image on a screen,speckles of a spot pattern are observed. One cause of the speckles isconsidered that, after a coherent light beam, a typical example of whichis a laser beam, is diffused on the screen, the coherent light beamgenerates an interference pattern on an optical sensor (retinas in thecase of human beings). Above all, when a coherent light beam is radiatedonto the screen by raster scanning, the coherent light beam is incidenton respective points on the screen from a constant incidence direction.Therefore, when the raster scanning is adopted, speckle wavefrontsgenerated on the respective points on the screen are unchanged as longas the screen does not swing, and when the speckle pattern is viewedwith an image by the observer, the image quality of a displayed image isdrastically degraded.

To the contrary, the transparent-type screen 40 of the transparent-typedisplay apparatus 10 according to the present embodiment changes thediffusion characteristics with time. When the diffusion characteristicsof the transparent-type screen 40 change, speckle patterns on thetransparent-type screen 40 change with time. When the diffusioncharacteristics change with time at a sufficiently high speed, thespeckle patterns are overlapped one another and averaged to be observedby the observer. Accordingly, speckles become inconspicuous.

The shown transparent-type screen 40 has a pair of electrodes 41 and 42.The pair of electrodes 41 and 42 are electrically connected to the powersource 30. The power source 30 is capable of applying a voltage to thepair of electrodes 41 and 42. When the voltage is applied between thepair of electrodes 41 and 42, an electric field is formed in theparticle sheet 50 located between the pair of electrodes 41 and 42. Theparticle layer 55 of the particle sheet 50 holds the particles 60 so asto be operable, each including the first part 61 and the second part 62different in dielectric constant. Since the particles 60 have beencharged or when an electric field is formed in at least the particlelayer 55, a dipole moment is generated, and hence the particles 60operate in accordance with a vector of the formed the electric field.When the particles 60 operate, which have a function of changing a lighttravel direction such as a diffusion function, as shown in FIGS. 27 to29, the diffusion characteristics of the transparent-type screen 40change with time. As a result, speckles become inconspicuous. In FIGS.27 to 29, a sign “La” is an image light beam radiated from the projector20 to the transparent-type screen 40 and signs “Lb” are image lightbeams diffused by the screen 40.

Concerning the difference in dielectric constants between the first part61 and the second part 62 of each particle 60, it is enough for thedielectric constants to be different to the extent that a specklereducing function can be exerted. Therefore, whether the dielectricconstants between the first part 61 and the second part 62 of theparticle 60 are different from each other can be determined by whetherthe particle 60 held so as to be operable can operate in accordance withthe change in electric field vector.

The operating principle of the particles 60 to the holder 56 is tochange the orientation and position of each particle 60 so that theelectric charge or dipole moment of the particle 60 has a stablepositional relationship with an electric field vector. Therefore, when aconstant electric field is continuously applied to the particle layer55, the operation of the particle 60 stops after a certain period oftime. On the other hand, in order to make speckles inconspicuous, it isrequired that the operation of the particle 60 to the holder 56continues. Accordingly, the power source 30 applies a voltage so that anelectric field formed in the particle layer 55 varies with time. In theexample shown, the power source 30 applies a voltage between the pair ofelectrodes 41 and 42 so as to invert the vector of an electric fieldgenerated in the particle sheet 50. For example, in an example shown inFIG. 7, the power source 30 repeatedly applies a voltage X[V] and avoltage −Y[V] to the pair of electrodes 41 and 42. Together with suchapplication of an inverted electric field, as an example, the particle60 can repeatedly operate between the states of FIGS. 29 and 27 with thestate of FIG. 28 as a center state. The voltage to be applied to thefirst and second electrodes 41 and 42 may not be limited to that shownin FIG. 7, which may, for example, be an alternating current voltage orthe like.

The particles 60 are accommodated in the cavities 56 a formed in theholder 56. In the example shown in FIGS. 27 to 29, each particle 60 hasan almost sphere outer shape. Each cavity 56 a that accommodates theparticle 60 has an almost sphere inner shape. Therefore, the particle 60can perform rotational vibration having a rotation axis line ra, as acenter, which extends in a direction perpendicular to the drawing sheetsof FIGS. 27 to 29. Depending on the size of the cavity 56 a thataccommodates the particle 60, the particle 60 performs, not only therepeated rotational vibration, but also translational motion. The cavity56 a is filled with the solvent 57. The solvent 57 makes smooth theoperation of the particle 60 to the holder 56.

In the present embodiment described above, the transparent-type screen40 has the particle layer 55 that has the particles 60 each includingthe transparent first part 61 and the transparent second part 62different in dielectric constant and the plurality of diffusedcomponents 66 b and 67 b diffused in the first part 61 and the secondpart 67 b, and has the electrodes 41 and 42 that form an electric fieldfor driving the particles 60 of the particle layer 55, by being appliedwith a voltage. In the transparent-type screen 40, when a voltage isapplied between the first electrode 41 and the second electrode 42, anelectric field is formed in the particle layer 55. In this occasion, theparticles 60 operate in accordance with the formed electric field. Whenthe particles 60 operate, which have a function of changing a lighttravel direction such as a diffusion function, the diffusioncharacteristics of the transparent-type screen 40 change with time.Therefore, while a light beam is being radiated onto thetransparent-type screen 40, by forming the electric field in theparticle layer 55 to operate the particles 60, it is possible toefficiently make the speckles inconspicuous. It is relatively easy toproduce such transparent-type screen 40, for example, using theabove-described production method. In addition, the transparent-typescreen 40 is suitable for a large screen and excellent in durability andoperational stability, and furthermore, easily-controllable.

Moreover, according to the present embodiment, the first part 61 and thesecond part 62 different in dielectric constant are formed to betransparent. Therefore, even though the orientations, postures, andpositions of the particles 60 change, the color of the transparent-typescreen 40 does not change. Accordingly, when displaying an image, it isnot perceived that the tone of the transparent-type screen 40 ischanged. As a result, it is also possible to efficiently avoid imagequality degradation in accordance with color change in thetransparent-type screen 40. The particles 60 operable in an electricfield and being transparent can be produced by forming the first part 61and the second part 62 from synthetic resins of the same kind and bymixing a chargeable additive into one of the first part 61 and thesecond part 62. Accordingly, this useful particles 60 for thetransparent-type screen 40 can be easily produced.

Furthermore, according to the present embodiment, while a light beam isbeing radiated onto the transparent-type screen 40, the particles 60 canbe repeatedly rotated in the particle layer 55. In other words, theparticles 60 can operate to effectively change the diffusioncharacteristics in an extremely small space. Therefore, by repeatedlyrotating the particles 60, while realizing a thin particle layer 55 anda thin screen 40, speckles can effectively be made inconspicuous.

As explained in the above-described embodiment, by varying theapplication voltage to the pair of electrodes 41 and 42, the particles60 can be operated. And, by adjusting the variation range, centervoltage, etc. of the application voltage, it is possible to control theoperation range of the particles 60 and the postures of the particles 60at the center of the operation range.

To the above-described embodiment, it is possible to make a variety ofchanges. Hereinafter, with reference to the drawings, an example ofmodification will be explained. In the following explanation and thedrawings to be used in the following explanation, the same signs asthose to the corresponding elements in the above-described embodimentare used and the duplicate explanation is omitted.

The first part 61 and the second part 62 of each particle 60 may bedifferent in volume ratio. In other words, the volume ratio of the firstpart 61 that occupies the particle 60 and the volume ratio of the secondpart 62 that occupies the particle 60 may be different from each other.

Ninth Embodiment

FIGS. 30 to 33 are illustrations for explaining a ninth embodiment ofthe present disclosure. FIG. 30 is an illustration showing a displayapparatus according to the present embodiment. FIG. 31 is anillustration for explaining an irradiation method of an image light beamonto the screen.

As shown in FIGS. 30 and 31, a display apparatus 10 is provided with aprojector 20 and a solar cell-equipped screen (photoelectric conversionpanel-equipped screen) 70. The solar cell-equipped screen 70 has ascreen 40 with a display-side surface 40 a to be irradiated with animage light beam from the projector 20 to display an image, and a solarcell panel (photoelectric conversion panel) 80. As described later, thescreen 40 is capable of changing with time the diffusion characteristicsthat affect an incident light beam. In this way, speckles becomeinconspicuous. The solar cell panel 80 is disposed at the opposite sideof the screen 40 to the display-side surface 40 a, to be irradiated witha light beam that has passed through the screen 40. In relation to suchfunctions of the screen 40 and the solar cell panel 80, the solarcell-equipped screen 70 further has a power supply device 30 and acontroller 35. The power supply device 30 generates an applicationvoltage based on power generated by the solar cell panel 80 and appliesthe application voltage to the screen 40. The power supply device 30may, for example, be a DC-AC converter to convert the power generated bythe solar cell panel 80 into an alternating current application voltage.The controller 35 controls the application voltage to control the modeof the screen 40.

The screen 40 according to the present embodiment has a particle sheet50 having a plurality of particles, and electrodes 41 and 42 connectedto the power source 30. The first electrode 41 is spread in a planarshape over one main surface of the particle sheet 50. The secondelectrode 42 is spread in a planar shape over the other main surface ofthe particle sheet 50. Moreover, the shown screen 40 has a first coverlayer 46 that covers the first electrode 41 to form one outermostsurface of the screen 40 and a second cover layer 47 that covers thesecond electrode 42 to form the other outermost surface of the screen40.

In the example shown, the screen 40 is a reflection-type screen. Theprojector 20 radiates an image light beam onto a display-side surface 40a made up of the first cover layer 46. The image light beam passesthrough the first cover layer 46 and the first electrode 41 of thescreen 40 and, thereafter, is reflected on the particle sheet 50 bydiffuse reflection. As a result, an observer situated to face thedisplay-side surface 40 a of the screen 40 can observe an image.

The particle sheet 50 has a pair of base members 51 and 52, and aparticle layer 55 disposed between the pair of base members 51 and 52.The particle layer 55 has a large number of particles 60 and a holder 56for holding the particles 60. Each particle 60 includes, for example, asshown in FIGS. 4 to 6, a first part 61 and a second part 62 different indielectric constant. Therefore, when this particle 60 is placed in anelectric field, an electron dipole moment is generated in the particle60. In this case, the particle 60 operates in such a manner that avector of the electron dipole moment is oriented in a complete oppositedirection of a vector of the electric field. Therefore, when a voltageis applied between the first electrode 41 and the second electrode 42,so that an electric field is generated in the particle sheet 50 locatedbetween the first electrode 41 and the second electrode 42, the particle60 operates in each cavity 56 a in such a manner that the particle 60takes a stable posture with respect to the electric field, that is, astable position and orientation with respect to the electric field. Thescreen 40 changes its diffusion characteristics in accordance with theoperation of the particles 60 having a light diffusion function.

Subsequently, the solar cell panel 80 will be explained. The solar cellpanel 80 is a power generator to convert light received at a lightreceiving surface 80 a into electrical energy. The light receivingsurface 80 a of the solar cell panel 80 may have an almost same area asthe area of an incidence-side surface 40 a of the screen 40. Moreover,it is preferable that the solar cell panel 80 is disposed at a positionat which most part of a light beam that has passed through the screen 40is incident on the light receiving surface 80 a. Because of thesefactors, power generation efficiency can be enhanced. The solar cellpanel 80 can take a variety of types of configuration. For example, asilicon-based solar cell including a flat silicon substrate made ofmonocrystalline silicon, poly monocrystalline silicon, etc., adye-sensitized solar cell, a thin-film solar cell, a chalcopyrite-basedsolar cell, etc. can be used as the solar cell panel 80. It ispreferable that conversion efficiency of the solar cell panel 80 ismaximum in a wavelength band of the light beam from the projector 20.

Subsequently, an operation in displaying an image using this displayapparatus 10 will be explained. The screen 40 of the display apparatus10 according to the present embodiment changes the diffusioncharacteristics with time. When the diffusion characteristics of thetransparent-type screen 40 change, speckle patterns on thetransparent-type screen 40 change with time. When the diffusioncharacteristics change with time at a sufficiently high speed, thespeckle patterns are overlapped one another and averaged to be observedby the observer. As a result, speckles become inconspicuous.

The shown screen 40 has a pair of electrodes 41 and 42. The pair ofelectrodes 41 and 42 are electrically connected to the power supplydevice 30. The power source 30 is capable of applying a voltage betweenthe pair of electrodes 41 and 42 based on power generated by the solarcell panel 80. When the voltage is applied to the pair of electrodes 41and 42, an electric field is formed in the particle sheet 50 locatedbetween the pair of electrodes 41 and 42. The particle layer 55 of theparticle sheet 50 holds the particles 60 so as to be operable, eachincluding the first part 61 and the second part 62 different indielectric constant. Since the particles 60 have been charged or when anelectric field is formed in at least the particle layer 55, a dipolemoment is generated, and hence the particles 60 operate in accordancewith a vector of the formed the electric field. When the particles 60operate, which have a function of changing a light travel direction,such as, a reflection function and a diffusion function, as shown inFIGS. 4 to 6, the diffusion characteristics of the screen 40 change withtime. As a result, speckles become inconspicuous. In FIGS. 4 to 6, andFIGS. 10 and 12 which will be referred to later, a sign “La” is an imagelight beam radiated from the projector 20 to the screen 40 and signs“Lb” are image light beams diffused by the screen 40.

Concerning the difference in dielectric constants between the first part61 and the second part 62 of each particle 60, it is enough for thedielectric constants to be different to the extent that a specklereducing function can be exerted. Therefore, whether the dielectricconstants between the first part 61 and the second part 62 of theparticle 60 are different from each other can be determined by whetherthe particle 60 held so as to be operable can operate in accordance withthe change in electric field vector.

The operating principle of the particles 60 to the holder 56 is tochange the orientation and position of each particle 60 so that theelectric charge or dipole moment of the particle has a stable positionalrelationship with an electric field vector. Therefore, when a constantelectric field is continuously applied to the particle layer 55, theoperation of the particle 60 stops after a certain period of time. Onthe other hand, in order to make speckles inconspicuous, it is requiredthat the operation of the particle 60 to the holder 56 continues.Accordingly, the power supply device 30 applies a voltage so that anelectric field formed in the particle layer 55 varies with time. Inother words, the controller 35 controls the application voltage so as tooperate the particles in the particle layer 55. In the example shown,the power supply device 30 applies a voltage between the pair ofelectrodes 41 and 42 so as to invert the vector of an electric fieldgenerated in the particle sheet 50. For example, in the example shown inFIG. 7, the power source 30 repeatedly applies a voltage X[V] and avoltage −Y[V] to the pair of electrodes 41 and 42. Together with suchapplication of an inverted electric field, as an example, the particle60 can repeatedly operate between the states of FIGS. 4 and 6 with thestate of FIG. 5 as a center state. The voltage to be applied to thefirst and second electrodes 41 and 42 may not to be limited to thatshown in FIG. 7, which may, for example, be an alternating currentvoltage or the like.

The particles 60 are accommodated in the cavities 56 a formed in theholder 56. In the example shown in FIGS. 4 to 6, each particle 60 has analmost sphere outer shape. Each cavity 56 a that accommodates theparticle 60 has an almost sphere inner shape. Therefore, the particle 60can perform rotational vibration having a rotation axis line ra, as acenter, which extends in a direction perpendicular to the drawing sheetsof FIGS. 4 to 6. Depending on the size of the cavity 56 a thataccommodates the particle 60, the particle 60 performs, not only therepeated rotary motion, but also translational motion. The cavity 56 ais filled with the solvent 57. The solvent 57 makes smooth the operationof the particle 60 to the holder 56.

In the present embodiment described above, the screen 40 has theparticle layer 55 that has the particles 60 each including the firstpart 61 and the second part 62 different in dielectric constant, and hasthe electrodes 41 and 42 that form an electric field for driving theparticles 60 of the particle layer 55, by being applied with the powergenerated by the solar cell panel 80. In the screen 40, when a voltageis applied between the first electrode 41 and the second electrode 42,an electric field is formed in the particle layer 55. In this occasion,the particles 60 operate in accordance with the formed electric field.When the particles 60 operate, which have a function of changing a lighttravel direction, such as, a reflection function and a diffusionfunction, the diffusion characteristics of the screen 40 change withtime. Therefore, while a light beam is being radiated onto the screen40, by forming the electric field in the particle layer 55 to operatethe particles 60, it is possible to efficiently make the specklesinconspicuous. It is relatively easy to produce such screen 40, forexample, using the above-described production method. In addition, thescreen 40 is suitable for a large screen and excellent in durability andoperational stability, and furthermore, easily-controllable.

Moreover, according to the present embodiment, since the solarcell-equipped screen 70 is provided with the solar cell panel 80, it canbe omitted to secure a separate power supply (commercial power supply orthe like) for driving the particles 60 of the particle layer 55 and toinstall wiring for power supply from the separate power supply to thescreen 40. Furthermore, since a light beam from the projector 20 is usedfor power generation, it is not required to radiate a separateillumination light beam for power generation or the like to the solarcell panel 80. Such solar cell-equipped screen 70 has high flexibilityin selection of installation place and hence applicable in a variety ofusage. That is, the solar cell-equipped screen 70 can be installed in aplace where it is difficult to secure a power supply, install wiring,etc., and a place where it is difficult to secure an illumination lightbeam for power generation.

Moreover, according to the present embodiment, each particle 60including the first part 61 and the second part 62 different indielectric constant is formed to have a monochrome color. Therefore,even though the orientation, posture, and position of the particle 60changes, the screen 40 has a constant color. Accordingly, whendisplaying an image, it is not perceived that the tone of the screen 40is changed. As a result, it is also possible to efficiently avoid imagequality degradation in accordance with color change in the screen 40.The particles 60 operable in an electric field and having a monochromecolor can be produced by forming the first part 61 and the second part62 from synthetic resins of the same kind and by mixing a chargeableadditive into one of the first part 61 and the second part 62.Accordingly, such useful particles 60 for the screen 40 can be easilyproduced.

Furthermore, according to the present embodiment, while a light beam isbeing radiated onto the screen 40, the particles 60 can be repeatedlyrotated in the particle layer 55. In other words, the particles 60 canoperate to effectively change the diffusion characteristics in anextremely small space. Therefore, by repeatedly rotating the particles60, while realizing a thin particle layer 55 and a thin screen 40,speckles can effectively be made inconspicuous. When repeatedly rotatingeach particle 60, its angular range is preferably less than 180° asshown in FIGS. 4 to 6. In this case, either of the first part 61 and thesecond part 62 can mainly be situated on the observer's side. In otherwords, while a light beam is being radiated onto the screen 40, it ispossible that the first part 61 covers at least part of the second part62 when viewed from the observer's side along the direction of normal ndto the screen 40. Accordingly, even if the first part 61 and the secondpart 62 do not have exactly the same color, during image display whileoperating the particles 60, it is possible that change in tone of thescreen 40 is hardly perceived.

As explained in the above-described embodiment, by varying theapplication voltage to the pair of electrodes 41 and 42, the particles60 can be operated. And, by adjusting the variation range, centervoltage, etc. of the application voltage, it is possible to control theoperation range of the particles 60 and the postures of the particles 60at the center of the operation range.

To the above-described embodiment, it is possible to make a variety ofchanges. Hereinafter, with reference to the drawings, an example ofmodification will be explained. In the following explanation and thedrawings to be used in the following explanation, the same signs asthose to the corresponding elements in the above-described embodimentare used and the duplicate explanation is omitted.

The light beam from the projector 20 may include a visible light beamand an invisible light beam. The invisible light beam may include atleast either of an infrared light beam and an ultraviolet light beam. Inthis case, the conversion efficiency of the solar cell panel 80 may bemaximum in a wavelength band of the invisible light beam. Accordingly,since the solar cell panel 80 can generate power with an invisible lightbeam, in addition to a visible light beam to be used for image display,large power can be generated. The range of choice can be enlarged forthe solar cell panel 80.

Moreover, the position at which the solar cell panel 80 is disposed isnot to be limited to that in the above-described example, which may be aposition that does not overlap with the screen 40 when viewed from theposition of the projector 20. That is, for example, as shown in FIGS. 32and 33, the solar cell panel 80 may be aligned with the screen 40 in theplane direction of the screen 40, so as to be irradiated with a lightbeam directly from the projector 20. There is no particular limitationon the actual position at which the solar cell panel 80 is disposed, theshape of the solar cell panel 80, etc. The solar cell panel 80 may bedisposed above, below, at the side of the screen 40, etc., when viewedfrom the observer, disposed above, at the side of the screen 40, etc.,in a shape of “L”, or disposed to surround the display-side surface 40 aof the screen 40. There is no particular limitation on the area of thelight receiving surface 80 a of the solar cell panel 80. However, sinceit is enough to generate relatively small power as described above, itis preferable that the area of the light receiving surface 80 a of thesolar cell panel 80 is smaller than the area of the display-side surface40 a of the screen 40.

As shown in FIG. 32, the projector 20 may radiate a first light beamformed with a laser light beam to the screen 40, and simultaneously withthis, may radiate a second light beam, which is in a wavelength banddifferent from the wavelength band of the first light beam, to the solarcell panel 80. The first light beam includes a visible light beam. Thesecond light beam includes at least either of a visible light beam andan invisible light beam. In other words, the projector 20 may include alight source for emitting the first light beam and a light source foremitting the second light beam, to repeatedly scan the entire area ofthe screen 40 with the first light beam and repeatedly scan the entirearea of the solar cell panel 80 with the second light beam. A rasterscanning projector 20 is capable of accurately scanning the entire areaof the solar cell panel 80 with the second light beam, with a small lossof the second light beam. With this kind of configuration, while thefirst light beam is scanning the display-side surface 40 a of the screen40, the solar cell panel 80 can continuously supply power to the screen40. It is preferable that the conversion efficiency of the solar cellpanel 80 is maximum in the wavelength band of the second light beam withwhich the solar cell panel 80 is irradiated. In this way, powergeneration can be performed efficiently.

The projector 20 may continuously radiate the second light beam onto apredetermined area of the solar cell panel 80, with no scanning of thesecond light beam. In this way, the configuration of the projector 20can be simplified. The second light beam may be or may not be formedwith the laser light beam.

Moreover, as shown in FIG. 33, the projector 20 may alternately radiatea light beam formed with the laser light beam onto the screen 40 and thesolar cell panel 80. Specifically, the projector 20 projects a coherentlight beam to repeatedly perform an operation of scanning the entirearea of the solar cell panel 80, after scanning the entire area of thescreen 40. In this case, the power supply device 30 is provided with acharging function of charging power generated by the solar cell panel80. Accordingly, while the screen 40 is being scanned, even if the solarcell panel 80 does not generate power, the power supply device 30 cansupply the power charged in the previous power generation to theelectrodes 41 and 42. The coherent light beam may include a visiblelight beam only or include a visible light beam and also an invisiblelight beam. Furthermore, the scanning direction is not to be limited tothat in the shown example, which may, for example, be a directionintersecting with the scanning direction of FIG. 33.

In the examples of FIGS. 32 and 33, the second electrode 42 may not betransparent. Therefore, the second electrode 42 can, for example, beformed with a metal thin film of aluminum, copper, etc. The secondelectrode 42 made of the metal film can also function as a reflectivelayer to reflect an image light beam in the reflect-type screen 40.

In the example shown in the above-described embodiment, the screen 40 isconfigured to be a reflective-type screen. However, not to be limited tothis example, in the case where the solar cell panel 80 shown in FIGS.32 and 33 is aligned with the screen 40, the screen 40 may be configuredto be a transparent-type screen. In the transparent-type screen 40, itis preferable that the second electrode 42, the second cover layer 47,and the second base member 52 may be configured to be transparent in thesame manner as the first electrode 41, the first cover layer 46, and thefirst base member 51, and have the same visible light transmittance asthat of the above-described first electrode 41, first cover layer 46,and first base member 51, respectively. Furthermore, it is preferablethat the quantities of the diffused components 66 b and 67 b to be addedin each particle 60 are adjusted so that transmittance to a light beamincident on the particle 60 becomes higher than reflectance to the lightbeam incident on the particle 60.

When the particles 60 are produced by the above-described microchannelproduction method, the first part 61 and the second part 62 may havedifferent volume ratios depending on the particles 60, so that theparticles 60 of different volume ratios may coexist. Even in such acase, the particles 60 rotate in the same manner by means of analternating current voltage applied to the first and second electrodes,and hence there is no particular practical problem.

In the example shown in the above-described embodiment, a positivelycharged monomer and a negatively charged monomer are used in syntheticresin polymerization to produce charged particles 60 of a monochromecolor. Not to be limited to this example, particles 60 having aplurality of parts of different charging characteristics in the solvent57 are composed by a variety of methods using conventional materials.For example, the particles 60 may be produced by forming a layeredstructure of two plate-like bodies of materials of differentperformances and crushing the layered structure into a desired size.Materials having the charging characteristics may be produced by, forexample, adding a charge control agent to synthetic resin. As an exampleof a charge additive, an ionic conduction additive that is a compound ofa polymer having polyalkylene glycol used for a static electricityinhibitor, as a main component, and lithium perchlorate or the like canbe adopted.

Furthermore, in the above-described embodiment, the particles 60 arespheres in the example shown. Not to be limited to this example, theparticles 60 may have an outer shape of rotary ellipsoid, cube,rectangular parallelepiped, conic solid, cylinder, etc. According to theparticles 60 of outer shapes other than the sphere, by operating theparticles 60, change in diffusion characteristics of the screen 40 withtime can be brought about, not by the inter diffusion function of theparticles 60, but by the surface reflection of the particles 60.

Moreover, the particle sheet 50, the particle layer 55, and theparticles 60 may be produced by methods different from the productionmethods explained in the above-described embodiments. Furthermore, aslong as the particles 60 are held by the holder 56 so as to be operable,the solvent 57 may not be provided.

In the above-described embodiments, one example of layered structure ofthe screen 40 is shown. However, not to be limited to the example,another function layer to be expected to exert a specific function maybe provided to the screen 40. One function layer may be configured toexert two or more functions. For example, the first cover layer 46, thesecond cover layer 47, the first base member 51, the second base member52, etc. may work as the function layer. As the function to be given tothe function layer, an antireflection (AR) function, a hardcoating (HC)function having excoriation resistance, an ultraviolet ray shielding(reflection) function, an anti-contamination function, etc. can belisted up as examples.

In the example explained in the above-described embodiment, theprojector 20 projects a light beam onto the screen 40 in the rasterscanning mode. However, not to be limited to the example, the projector20 may, for example, project an image light beam onto the entire area ofthe screen 40 at each moment in a mode other than the raster scanningmode. Speckles are generated even when such a projector 20 is used.However, using the above-described screen 20, diffusion front on thescreen 40 changes with time to make speckles inconspicuous efficiently.Moreover, the above-described screen 20 can be used in combination withthe projector disclosed in International Publication 2012/033174explained in BACKGROUND ART, that is, a projector capable of changingthe incidence angle of an image light beam on each position on thescreen with time. According to this projector, speckles can effectivelybe reduced, however, when this projector and the above-described screenare combined, speckles become inconspicuous more effectively.

Furthermore, in the example shown in each above-described embodiment,the first electrode 41 and the second electrode 42 are formed in aplanar shape and arranged to sandwich the particle layer 55. Not to belimited to this example, one or more of the first electrode 41 and thesecond electrode 42 may be formed into a stripe pattern. For example, inthe example of FIG. 34, both of the first electrode 41 and the secondelectrode 42 are formed into a stripe pattern. In other words, the firstelectrode 41 has a plurality of linear electrode parts 41 a extending ina straight line, the plurality of linear electrode parts 41 a beingarranged in a direction perpendicular to its longitudinal direction.Like the first electrode 41, the second electrode 42 has a plurality oflinear electrode parts 42 a extending in a straight line, the pluralityof linear electrode parts 42 a being arranged in a directionperpendicular to its longitudinal direction. In the example shown inFIG. 34, the plurality of linear electrode parts 41 a that constitutethe first electrode 41 and the plurality of linear electrode parts 42 athat constitute the second electrode 42 are both arranged on a surfaceof the particle sheet 50 opposite to the observer's side surfacethereof. Moreover, the plurality of linear electrode parts 41 a thatconstitute the first electrode 41 and the plurality of linear electrodeparts 42 a that constitute the second electrode 42 are alternatelyarranged along the same arrangement direction. Also with the firstelectrode 41 and the second electrode 42 shown in FIG. 34, by applying avoltage from the power source 30, an electric field can be formed in theparticle layer 55 of the particle sheet 50.

Several modifications to the respective embodiments described above havebeen explained, however, it is a matter of course that a plurality ofthe modifications can be combined to be applied.

1. A light diffusion sheet comprising a plurality of particles whichcomprise a first part and a second part, the first part and the secondpart being held so as to be operable, wherein the first part and thesecond part in at least one of the particles comprise a base materialcomprising resin and a plurality of diffused components dispersed in thebase material, and light intensity distribution on a measuring surfacechanges with time in accordance with operation of the particle.
 2. Thelight diffusion sheet of claim 1, wherein the diffused componentcomprises at least one of resin beads, glass beads, a metal compound, aporous material containing a gas, and bubbles.
 3. The light diffusionsheet of claim 1, wherein dielectric constants of the first part and thesecond part of the particles are different from each other.
 4. The lightdiffusion sheet of claim 1, wherein the particles have a monochromecolor.
 5. The light diffusion sheet of claim 1, wherein either of thefirst part or the second part of the particles is transparent.
 6. Thelight diffusion sheet of claim 1, wherein a volume ratio of the firstpart of the particles is larger than a volume ratio of the second partof the particles.
 7. A screen which displays an image by beingirradiated with a light beam from a projector, comprising: the lightdiffusion sheet of claim 1, and electrodes which form an electric fieldin accordance with a voltage applied to a particle layer of the lightdiffusion sheet, the electric field driving the plurality of particles.8. A screen of claim 7 further comprising a Fresnel lens layer disposedon a surface side of the particle layer, the light beam being incidenton the surface side.
 9. A display apparatus comprising: a projectorwhich emits a coherent light beam; and the screen of claim
 7. 10. Thedisplay apparatus of claim 9 further comprising: a power source whichapplies a voltage to the electrodes of the screen; and a controllerwhich controls an application voltage from the power source to theelectrodes, wherein the controller controls the application voltage ofthe power source so as to operate the particles in the particle layer.11. The display apparatus of claim 9, wherein the controller controlsthe application voltage so as to repeatedly rotate the particles withinan angular range less than 180°.
 12. The display apparatus of claim 9,wherein the controller controls at least orientations or positions ofthe particles by the application voltage of the power source so that thefirst part covers at least part of the second part from an observer'sside along a direction of normal to the screen.